Increasing both power and fuel economy at the same time is like going out on a date with Scarlett Johansson and having her pick up the check. Yet this is just what the 2008 Chevrolet Tahoe Hybrid accomplishes thanks to General Motors' first full-fledged hybrid system known as "Two-Mode." While other GM models have donned the hybrid badge, the Tahoe and its sister GMC Yukon hybrids are the first to feature sizable electric motors capable of propelling the vehicle without the gas engine. The result is a full-size SUV capable of fuel economy in the 20s, that also carries eight people and can tow a 6,000-pound trailer.

At the heart of the Tahoe Hybrid is the "Two-Mode" technology co-developed by GM, BMW and DaimlerChrysler. A 6.0-liter V8 with cylinder-deactivation technology serves as the gasoline engine, while a pair of 60-kilowatt motors packaged within the transmission provide the all-electric motivation. Dubbed an electrically variable transmission (EVT), the Tahoe's transmission features those two motors, three planetary gearsets and four traditional hydraulic wet clutches.

The EVT is essentially like having two transmissions inside one -- continuously variable drive for light load conditions and fixed-ratio for high load conditions. Hence two-mode. The hybrid system then constantly determines the most fuel-efficient means of propelling the vehicle -- be it electric power, gasoline power or a combination of the two. And like other hybrid models, there's a battery pack for storing power, regenerative braking to take advantage of the vehicle's momentum and the ability to shut off the engine when the vehicle is stopped.

The moral of the above story is that this 5,600-pound full-size SUV returns fuel economy better than most large crossovers. City mileage is particularly impressive, and like most hybrids, is about equal to highway mileage. This is the result of being able to accelerate up to approximately 25 mph using electricity only, a fuel-saving asset on surface streets and in stop-and-go traffic. If that's your driving domain, the Tahoe Hybrid makes a lot of sense.

In addition to improved fuel economy, the 2008 Chevrolet Tahoe Hybrid boasts more power than its gas-only brother. However, don't expect much better acceleration, as the hybrid tips the scales at a hundred or more pounds heavier than a fully loaded Tahoe LTZ. That's despite Chevy's best efforts to cut weight by constructing several body panels of aluminum and trimming heft from the seats (though ironically not from the heavy removable third-row seats, which could easily benefit from a nip and tuck).

Other than its sophisticated running gear, the Tahoe Hybrid is essentially a fully loaded Tahoe LT. The only options are a sunroof and DVD entertainment system, with niceties like leather, a rearview camera and navigation system standard. However, the price premium is significant, ringing in at about $8,000 more than a similarly equipped gas-only Tahoe. Although the fuel economy difference is also pretty hefty, it's hard to say if your gas savings will justify the out-the-door premium. We'll let you decide if the environmental benefits are worth the price, but how green can a 5,600-pound SUV ever be?

So, unless the 2008 Tahoe Hybrid's significant towing capabilities are important, a full-size crossover like the Buick Enclave or GMC Acadia may be a better choice. They provide more usable passenger space, they're friendlier to drive, get close to the same fuel economy and are $10,000 cheaper when fully loaded. The new two-mode hybrid system is certainly impressive, but we're not entirely sure if the Tahoe is the right vehicle for it.

The 2008 Chevrolet Tahoe Hybrid is a full-size SUV available in one trim level. Standard equipment is extensive and includes 18-inch alloy wheels, rear parking assist with rearview camera, tinted windows, power-folding heated side mirrors, tri-zone automatic climate control and a trip computer. An auto-dimming rearview mirror, remote engine start, leather upholstery, power front seats, a removable 50/50-split third-row seat, OnStar, a navigation system and a hybrid system display are also standard. The Bose audio system comes with nine speakers, a CD/MP3 player, an auxiliary audio jack, two rear seat headphone jacks and satellite radio. A sunroof and rear-seat DVD entertainment system are the lone options.

The 2008 Chevy Tahoe Hybrid utilizes a 6.0-liter V8 engine coupled to a pair of 60-kilowatt electric motors located inside what GM calls an electrically variable transmission. Together, they produce 332 horsepower and 367 pound-feet of torque. Both rear-drive and four-wheel-drive versions are offered.

The system can accelerate the Tahoe up to speeds of approximately 25 mph using electricity only, while the V8's cylinder-deactivation system helps reduce fuel consumption at higher speeds. Regenerative braking replenishes the batteries by capturing energy normally lost when coming to a stop. Fuel economy is 21 mpg city and 22 mpg highway for rear-wheel-drive Tahoe Hybrids and 20/20 with 4WD. Properly equipped, a 4WD Tahoe Hybrid can tow 6,000 pounds.

Standard safety equipment includes full-length side curtain airbags, antilock disc brakes, traction control, OnStar and a rearview camera. In government crash testing, the 2008 Chevrolet Tahoe Hybrid scored a perfect five stars in all frontal and side tests.

It's not a stretch to say that driving the 2008 Chevrolet Tahoe Hybrid feels like being behind the wheel of a 5,600-pound Prius. There's the same eerie quiet when accelerating and braking, as the gas engine shuts off to let the electric motors do their thing. Although a tad strange, the result is a quiet cabin, while transitions between gas and electric modes, and eight- and four-cylinder power delivery, are either undetectable or easy to ignore.

The regenerative braking system produces a firm braking feel and, according to GM, actually stops the big SUV better than the regular Tahoe's conventional brakes do. Although the Hybrid is the most powerful Tahoe available, it's also the heaviest, so don't expect particularly brisk acceleration. Still, its abundance of low-end power -- aided by those torque-rich electric motors -- proves ample for around town and trailer towing.

Aside from instrumentation, there's nothing to distinguish the Tahoe Hybrid from a loaded regular Tahoe. Unlike past generations, that's a very good thing. The newest Tahoe boasts attractive high-quality materials and tight build quality, while maintaining a simple control layout. Even the standard navigation system is easy to use.

With its standard third row, the Tahoe can seat up to eight passengers. Unfortunately, that 50/50 third row does not fold flat into the floor. Since the two seats weigh more than 60 pounds each, you'd better have an American Gladiator on standby to help remove them. Once they're out, though, maximum cargo capacity is a whopping 109 cubic feet with the second-row seats down -- much more than any other hybrid offers.