I'm only half white. The other half? Irish. In addition to some odd shocks of red hair and freakish dentition, this manifests itself in other strange ways, not the least of which is an inability to back down from a challenge, even if it's blitheringly obtuse. I'm also an auto writer, which means that freebies are the hamster that drives the wheel of my enterprise. So when General Motors flew a group of us journalists out to La Jolla, California, for a chance to win a free iPod by recording the best mileage in a Chevy Tahoe Hybrid, it couldn't have been a better fit for me had it been turned on the lathe of the gods.

The Tahoe Hybrid is the first model from GM to use its "2-Mode" hybrid system. Developed in collaboration with Chrysler and BMW — a similar system will be appearing on the Dodge Durango and the BMW X6 — the 2-Mode hybrid is supposed to boost fuel economy when plodding around town, but is also designed to make the vehicle more efficient on the highway, an area where many current hybrids fall down. But how does it work? Will it live up to the promises? That's what I was going to find out, and I was hoping to score some free swag in the process.

At our drivers' meeting, I was already formulating a plan of attack — sketch out for me the basis for a contest, and I am programmed by a lifetime's worth of practice to discover the loopholes and exploit them. The more restrictive the rules, the harder I work to bend them to my advantage. "You must pair up with another journalist," we're told by an organizer, "and you'll each drive one half of the route." Excellent, just allow me to find the smallest, lightest person here. "Participants can't pump up the tires with more air; we'll check them when you stop at the halfway point." Well, you didn't say anything about shutting the engine off and coasting, did you? "Drivers can't fold in the mirrors for better aerodynamics." Not a problem, as aerodynamics aren't an issue when drafting five feet off a semi truck.

Then the body blow: "A GM representative will ride along to make sure you're staying within the spirit of the rules." But all was not lost, as I managed to find a spry little Canadian co-driver who looked like he fell off a charm bracelet and couldn't have weighed an ounce over 120. I also had a secret strategy that I'd wheedled out of a GM powertrain engineer, a strategy that I ran through my head as we filtered out into the parking lot, committing it to memory as I picked out a particularly evil-looking black 2WD Tahoe from the lineup of trucks we could use. By pressing hard and holding down on the brake pedal, he'd told me, I could disable "creep torque," a feature programmed into the hybrid driveline that inches the SUV forward at idle using its electric motor. With the only light pressure on the brake pedal, the electric motor is always trying to roll out, simulating the feel of a torque converter and sapping precious electricity from the Tahoe's 300-volt battery pack, which rests under the butt of the GM watcher now sitting in my ute's middle row.

An event staffer recorded the vehicle's mileage, reset the trip computer, and motioned for me to set off. The gauntlet had been thrown down, the die was cast, the condom foil torn. Game on.

I feathered the throttle and the Tahoe rolled forward from its parking spot in dead silence. This, as I'd learn later, was the first mode of the 2-Mode hybrid system, the one specifically designed for low speeds. The Tahoe Hybrid will start off on full electric, even if loaded down with its full 6000-pound trailer weight. It has to; there's no torque converter between the engine and transmission, only a fully on or fully off hydraulic clutch, so the SUV needs to be in motion before coupling the two together. Up to 30 mph, the vehicle can be propelled entirely by electric power, with the engine completely shut off and uncoupled from the driveline. Or the gas engine can drive the Tahoe Hybrid through the transmission's four forward gears, like a normal truck does, with the electric motor shut off. Or, and this is where GM says that 75 percent of the first-mode driving will happen, the engine can propel the ute, with the electric motor providing assistance as it deems fit.

The side streets of La Jolla, with their 25-mph speed limits, provided the perfect opportunity to exploit the Tahoe's electric-only mode to my advantage. Gingerly working the pedal and staring at the power-flow display on the dash-mounted LCD, I was maximizing every milliamp at my disposal from the Tahoe's battery to keep the gas engine from coming to life, a process that is — to other motorists — indistinguishable from simply dicking about. I was able to keep the Tahoe running on electric power only as it skimmed down the road in perfect, phantom silence, a three-ton black hole passing by unnoticed.

The only sound the Tahoe makes, in fact, is a soft, permeating, technological whir from its electric drive. Even that could have been eliminated, I was told by Gary White, GM's vice president of full size truck lines, "but people really liked hearing the whine." That or GM's suppliers weren't cutting deals on sound blankets that week. But White swore that the electric thrum made drivers feel like they were driving a piece of high technology.

Once the road widened to two lanes, however, all that was audible were the sounds of cars under hard kickdown as the conga line that queued up behind me pulled around to pass. A silver Prius with a conspicuous "Hug Your Mother (Earth)" bumper sticker slinked past, its driver extending a long, skeletal digit that I'm going to assume means I was number one in her book. Mouths went wide and then round in my rearview mirror, forming the predictable two-syllable epithet. Screw 'em; I was in the employ of more important things, and according to the trip computer, I'd averaged 28.7 mpg over the first three miles.

Then, tragedy struck. I had been driving as if I had no brakes, coasting as long as possible, letting the SUV slow itself down. But after three and a half miles, the Tahoe's battery had given its last. The gas engine burbled to life. With the 6.0-liter engine ticking over, the display showed that the V8 powerplant alone was propelling the truck, while the electric motor was given entirely to running as a generator, charging the batteries. At the next stoplight, even with the brake pedal pinned down to banish creep torque, the engine kept idling. I executed what hybrid geeks call a "forced auto-stop," which the rest of us know as "turning the key off." Killing the V8 couldn't come soon enough: After just a few blocks of operation, the trip computer showed my average economy had backslid to 23.2 mpg.

I made up for this later on, rolling down hills where I could, pitching the Tahoe into hard turns faster than I thought possible, letting the StabiliTrak take over where my skill ran out, and hearing the cries of the low-rolling-resistance tires. In situations like this, the Tahoe's hybrid system shuts the engine off entirely, letting me coast through a green light, through a yellow light. To say that I was reducing friction is to insult ball bearings. The trip computer crept back up to 25.1 mpg. My first-place prospects were looking sunny.

Which, of course, was an excuse for everything to go all to hell again, as our route took a turn onto the highway. Hybrids are at a disadvantage on thoroughfares because their gas engines need to be running to maintain speed. Compounding the problem is that the massive torque of electric motors, which is greatest at low speeds, peters out as they run faster. This is where the second mode of GM's hybrid system comes into play: Rather than rely on just one motor for all occasions, GM installed a second electric motor in the Tahoe's transmission — geared specifically to help move the truck on the highway — so that the motor can turn at a slower, and thus more efficient, speed.

The second motor is also designed to work in concert with the Tahoe Hybrid's 332-horsepower V8 engine. "Active fuel management," as Chevy calls it, shuts off two cylinders on each bank, letting the 6.0-liter V8 operate as a 3.0-liter V4 for most of its highway cycle. The second-mode electric motor adds up to 80 horsepower on demand, keeping the engine running on four cylinders as long as possible. The system works so well that GM discovered installing its smaller 5.3-liter V8 was counterproductive. The smaller engine's four-cylinder mode didn't have enough torque to push the truck through the air, requiring it to run in eight-cylinder mode more frequently and dragging down its fuel economy.

It's been said that hybrids require an entirely different approach to driving, and that's partly true with this Tahoe. Not because the actual act of driving requires you to be bent to the Tahoe's will, but because its instantaneous mileage display broadcasts the results of poor driving in glowing green shame. There's nothing dynamically different driving the hybrid and a regular Tahoe — GM has so thoroughly integrated the electronics that the daft won't have a clue as to what their foot's commanding, controlling, or compelling. But even those drivers will have a Pavlovian response to the gauge, taking off just that little bit more slowly, driving just a little bit less urgently, to maximize the numbers it reports. Despite feeding the throttle little baby inputs, the slightest call for acceleration brings the engine up to V8 mode. When that happens, the gauge drops into the single digits, fuel getting sucked down as though in a beer bong. The display couldn't cow drivers for fear of ignominy any better if it had been invented by a Jewish mother.

Around me, the other four lanes were full of drivers weaving erratically, accelerating hard until they'd nearly violated the car in front of them, and then pegging their brakes. To watch them was to see madness in motion, and I was chuckling as they fed their cars completely digital inputs — on or off, all or nothing. I was immune to the surrounding chaos, having a Zen moment in the right lane, riding the white line so the Tahoe's tires ran outside of the rougher, higher-friction ruts. The speed limit was 55, but I was holding 50. A competing Tahoe Hybrid inched past and I tucked in behind it, letting the lead vehicle plow through the air for me. I couldn't tell if my junior NASCAR drafting was helping mileage or not. What I could tell, after twenty minutes with no air conditioning, was that my shirt was sticky.

Even without shamelessly taking advantage of the leader, the Tahoe Hybrid cuts a sleeker path through the atmosphere than normal models. The smooth front bumper is devoid of holes for foglights and tow hooks, and the lower air dam is designed to channel flow around its gaping wheelhouse openings. The D-pillars are squared off to help reduce turbulence around the tailgate, and the taillamps run LEDs instead of bulbs, which the General says are good for 0.2 mpg just because of their reduced electrical load.

The rest of the changes are even harder to discern: The hood is stamped out of aluminum, as is the liftgate, which most buyers won't discover until their magnetic ribbons won't stick. The spare tire's been tossed in favor of an inflator kit, and the front seats are 1.5" thinner to reduce mass. The hybrid drivetrain and battery adds 400 pounds, but the lightweight changes are enough to offset 100 of those.

So with an extra 300 pounds to lug about, it's only reasonable to assume that the Tahoe Hybrid takes a while to stop. Except that it doesn't — GM says the Hybrid, with four-wheel discs and ABS, actually hauls itself down to zero in less distance than the gas-only model. Which is all the more impressive when you realize that there's no physical connection between the brake pedal and what happens at the wheels. The utes use a brake-by-wire system so stepping on the pedal just works a sensor, and a pedal-effort simulator presses back with the amount of resistance drivers would expect from a normal braking system. Sensing a decelerative event, the engine control computer throws the hybrid driveline into full regenerative braking, reversing the flow of current from the hybrid drive motors and using them as generators to charge up the battery pack. It requires a hefty amount of power to turn a generator that's at full boil, so the transmission-mounted motors act as a brake on the driveshaft, slowing the truck down. The Tahoe's body computer then reads how hard you're stomping on the dummy pedal and calculates three things: How much the truck is slowing down from the regenerative braking, how quickly a regular Tahoe would stop if you were pressing on a traditional brake pedal that hard, and how much it would need to apply the truck's hydraulic brakes in addition to the regenerative setup to slow the truck down at a rate that most drivers are expecting. The result is that the Tahoe Hybrid recharges its batteries when slowing down, without any obvious changes in pedal effort or the SUV's dynamic behavior.

In addition to the electric brakes, the Tahoe Hybrid's power steering is fully electric, with a small motor mounted on the steering rack. GM's previous electric-assist systems, which found their way onto all manner of cars and light trucks, would allow whole lane changes through a light flexing of the fingers, but the new setup gives decent feedback and has a fair amount of heft behind it, just like a the hydraulic setup on the regular Tahoe. The hydraulic power steering pump was laid on the altar, GM says, in the name of efficiency. Taking the load off the engine bumps mileage by 0.5 mpg, and further parasitic losses are sent packing by Tahoe Hybrid's 300-volt air-conditioning system that drives the compressor with an electric motor, just like the window unit in your first apartment.

My time behind the wheel ended next to Naval Base San Diego, where the aircraft carriers stood proudly against the horizon and were dwarfed by the megalopolis cruise ships moored further down the coastline. Gliding toward the entrance to our designated rest area, coasting down to 30 mph, then 25, then 20, with my left signal on all the way, I eased the Tahoe into the highest parking slot there, its nose forward so it could coast out with no fuel wasted backing up. Over the 30.5-mile run, the full-size SUV returned 24.8 miles per gallon, a figure that GM's reps were quick to point out bests that of a four-cylinder Toyota Camry. As a GM employee dutifully recorded our mileage, he let slip that my figure was tied with one other truck for first place.

I knew our competitor didn't stand a chance. I had a secret weapon. He was Canadian, and any man from a country that can teach Frenchmen to play hockey doesn't have much outside the scope of his national acumen. Switching seats, I began plotting the playlists I wanted to load on my new iPod for the flight home.

The Greeks called it "hamartia" — a fatal flaw that bides its time, like a renegade gene, until the exact moment when it can bring an otherwise healthy individual to his knees. Hamartia could be anything: pride, perhaps, or, in this case, traffic on California's 805 during rush hour. The highway was uphill and packed with an endless torrent of stationary cars, each passenger-less driver a raindrop believing that he wasn't responsible for the flood. The Tahoe's cooling fan, which up to this point had stayed unobtrusively off, roared on to keep the liquid-cooled hybrid power module under the hood from overheating, which necessitated waking the engine up to charge the battery. The lane to the left of our truck was crawling steadily forward, and through the side window I watched seven other teams in their Tahoes creep past, an experience that inspired the same helpless horror as witnessing a crime committed on a security monitor. The fuel-economy gauge in the cluster mercilessly adjusted itself downward.

Forty minutes later, our truck was one traffic signal away from the hotel when the light clicked over to yellow. We had plenty of time to make it through. The car behind us had plenty of time to make it through. The bus behind that car had plenty of time to make it through. But my relentlessly polite Canadian co-driver wouldn't have it, putting the Tahoe up on tiptoe to avoid as potentially serious a grievance as running a yellow. "Whoopsydaisy!" he called out as the Tahoe settled back on its haunches. Heaping insult upon my injury, the engine sprang to life as the cooling fan, again, mockingly spun up.

All told, my team fell from first-place contender to the one everyone assumed had gotten lost along the way. But even though our aggregate mileage ended up being the worst of every team competing, including the 4WD models, we still managed to return 22.7 mpg — hardly shabby by any yardstick. But — and here's the take-away from this entire fiasco — the Tahoe returned over 20 mpg when driven like a normal truck. Stop and go. Racing up to stop lights and slamming on the brakes. GM's optimized the way the hybrid system works to compensate for the way people drive, so the only thing I got in exchange for all of the hypermiling crap was only a few miles per gallon more, and a lot of screamed epithets and aerated spittle that informed me I have an Oedipus complex.

At $50,490 for the 2WD model (4WDs will set you back an extra $2800), a Tahoe Hybrid is $4000 more than a top-line non-hybrid Tahoe LTZ. And while it's tempting to lambaste GM for not offering a diesel instead, remember that the price premium for the hybrid is around $3000 cheaper than GM's Duramax option in its full-size trucks, which won't fit on the Tahoe's half-ton chassis anyway. If you're not serious about towing, a larger GMC Acadia will return better highway mileage for nearly $14,000 less. But for those with trailers, those with boats, those — in short — who need a truck with some mass to it, the Tahoe Hybrid merits serious consideration.

Hypermiling Like a Pro

Wayne Gerdes has been called the "King of the Hypermilers" by Mother Jones magazine. He is also the winner of the 2006 HybridFest MPG Challenge in Madison, Wisconsin, averaging 180.1 mpg from a three-cylinder Honda Insight. He offers the following tips for extreme hypermiling on his website, CleanMPG.com. Many of his tips are illegal, most are dangerous, and nearly all of them will have other drivers accusing you of having an improper relationship with a goat. But the results can't be argued with. Try these at your own, and your license's, risk.

Forced Autostop (FAS): When coasting towards a stop, some hybrids will automatically shut down their internal-combustion engines. You can force a shutdown by turning the ignition off, and then clicking it back to "on" — but not restarting the engine.

Draft-Assisted Forced Autostop: When ready to execute an FAS, select a target vehicle, like a large truck, that's going slightly slower than you. Kill the engine and glide up behind the truck. The truck will cut through the air so you don't have to, prolonging the time you can go before restarting the engine.

Pulse and Glide: After accelerating the vehicle to a target speed, shut down the engine and allow the car to coast, in neutral, down to a lower speed, at which point you restart the engine and reaccelerate to your target speed and repeat the process. By increasing your target speed and restart threshold by 5 mph each time, you can work your way up to higher speeds without the same mileage hit as going all out.

Driving Without Brakes: Mentally discipline yourself to imagine that your car has no brakes. You'll become more situationally aware, timing traffic lights so they turn green just as you roll through them and leaving a large enough gap to absorb variations in speed between you and other cars on the road.

Driving With Load: Instead of trying to maintain a steady speed while going up hills, try to maintain steady fuel consumption using the real-time economy gauge in your car's trip computer. Your car will slow down slightly when climbing the grade, but you'll make up the speed once you crest it.

Rabbit Timing: On lightly trafficked roads, anticipate when the cars far ahead of you will trigger the traffic lights to change, so you can glide through the intersection without having to stop.

Smart Braking: When heading up an incline, you want to use up every bit of inertia you have to stop as high up as possible. When you restart and begin to roll out, you'll have to cover less of the treacherous grade that way. On a decline, stop as high up as possible as well. When you take off, coast for as long as you can before restarting the engine.

Potential Parking: When parking, seek out the highest spot in the parking lot. When you go to leave, you can coast for a while and pick up speed before turning the engine on. This often means you'll have to park away from the front door, but losing a few pounds will help your fuel economy anyway, tubby.