Overview. With large-vehicle sales hurt by high fuel prices, does a hybrid-powered full-sized SUV make sense right now? Only if you plan to do a lot of driving and truly need its abilities.

We are testing GM's new full-hybrid version of the Chevrolet Tahoe, which is powered by a 332-hp, 6.2-liter V8, two electric motors and a large nickel-metal-hydride battery pack. Our well-equipped Tahoe Hybrid cost $55,585—about $7,000 more than a comparable Tahoe LT with a 5.3-liter V8. According to GM, the hybrid has "limited availability," which might preclude the large incentives and haggling that's available on the regular Tahoe.

Besides the electric part of the powertrain, significant changes were made by GM to the hybrid Tahoe and its cousin the GMC Yukon to help to save fuel. Notably, those include a continuously variable transmission, and the body was lowered for better aerodynamics. Some body panels are lightweight aluminum. The rear-axle ratio was made taller, so the engine can rev slower at highway speeds. A cylinder deactivation system shuts off half the cylinders when they're not needed at cruising speeds. And like other hybrids, this one uses regenerative braking to help charge the battery, and the engine shuts down when you stop, for example at a red light.

We calculate that those changes improve fuel economy by about 35 percent compared with a regular Tahoe LT. So far, we've been averaging about 19 mpg overall. A comparable Tahoe LT gets about 14 mpg. In 15,000 miles, then, the hybrid would use 282 fewer gallons of gas, which at $4 per gallon amounts to $1,128 savings. That's certainly significant, but it would still take close to 100,000 miles of driving on $4 gas to recover the extra purchase price of the hybrid.

Initial impressions. Driving the Tahoe Hybrid is a lot like driving a regular Tahoe. Acceleration feels strong. In stop-and-go driving the driveline sometimes makes rough transitions between electric and gas-engine modes. Some drivers noticed a whining noise when braking that sounds like distant sirens. The stiff brake pedal can make it difficult to stop smoothly. The electric steering also feels a bit vague, and the ride, fairly supple and well controlled, feels a little stiffer than in a regular Tahoe.

Some fuel-saving strategies compromised function. The lowered ground clearance and big front air dam makes the hybrid more vulnerable to damage while off-roading. There's no power seat recline, an odd omission in a $55,000 vehicle. There's also no spare tire, only an inflator kit and a can of sealant, and no roof rack.

CR's take: There are two primary practical reasons to buy a large SUV in the first place: it can fit a lot of people and tow heavy loads. The Tahoe's third-row seat is cramped and uncomfortable, though, and leaves little cargo space behind when in use. Several car-based SUVs, such as the Honda Pilot (17 mpg) or Saturn Outlook/GMC Acadia (16 mpg) offer better accommodations and cost $15,000 to $20,000 less.

If fuel economy is high on your priority list and a midsized SUV suits your needs, then you might consider the Toyota Highlander Hybrid ($44,000 in Limited trim). It's a much more refined vehicle overall than the Tahoe and averages 24 mpg.

As for towing, the Tahoe Hybrid's maximum towing capacity, 6,000 pounds, is quite respectable and 1,000 to 1,500 greater than that of the largest car-based SUVs, but 2,200 pounds less than that of a regular Tahoe. All in all, the price difference would likely approach an additional $10,000 to buy the hybrid—that buys a lot of fuel.

The Tahoe Hybrid's various compromises offer fewer of the attributes that lead buyers to buy such large vehicles in the first place. But the technologies are commendable, and it would be good to see them employed in other GM vehicles.

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