If you have owned a full-size SUV, chances are pretty good that fuel mileage of 15 mpg or less was a way of life. But that's not so with the 2012 GMC Yukon Hybrid (or its Chevy Tahoe Hybrid twin), as it's rated at 21 mpg in combined city/highway driving. Apart from its powertrain, the Yukon Hybrid is functionally little different from a standard Yukon, meaning you still get a powerful V8, the ability to transport up to eight people and a towing capacity of 6,200 pounds.

To achieve this level of fuel efficiency in a 5,600-pound, truck-based SUV, the Yukon's 6.0-liter V8 engine works in concert with a hybrid system that features two 60-kilowatt electric motors packaged within the transmission. The latter is rather complex, as it is essentially like having two transmissions inside one -- a continuously variable drive unit for light load conditions and a standard four-speed fixed-gear type for high load conditions.

As such, the Yukon Hybrid can (under low-load conditions) move solely under electric power up to speeds of around 25 mph, hence its impressive city fuel economy rating of 20 mpg. For comparison, a standard Yukon 2WD with the 6.2-liter V8 rates just 14 mpg in the city. To minimize the weight gain associated with all that hybrid hardware, several body panels are made of aluminum and even the seats have been slimmed down. Sadly, the heavy and awkward-to-remove third-row seats didn't take part in the diet.

Though the 2012 GMC Yukon Hybrid cuts down on fuel expense and the consumption of a finite resource, it's still going to cost you. With pricing in the low-$50,000 range when new, you're looking at a considerable premium over a non-hybrid Yukon. More to the point, you're looking at a huge premium over a lighter and better-handling crossover SUV that offers similar or greater passenger/cargo room and fuel efficiency. And then there's the Yukon Hybrid's heavy and complex powertrain to consider.

So, unless the 2012 GMC Yukon Hybrid's significant towing capabilities are beneficial to you, full-size crossovers like the Ford Flex, GMC Acadia or Mazda CX-9 are likely better choices. You should also take a look at the Toyota Highlander Hybrid (it's not as brawny, but it's cheaper and more fuel efficient) or smaller but similarly priced diesel-powered three-row crossovers like the Audi Q7 TDI and BMW X5 xDrive 35d that provide greater fuel efficiency and a superior driving experience.

The 2012 GMC Yukon Hybrid is a full-size SUV available in one trim level.

Standard equipment includes 18-inch alloy wheels, rear park assist with rearview camera, tinted windows, power-folding heated side mirrors and tri-zone automatic climate control. A trip computer, Bluetooth, OnStar, an auto-dimming rearview mirror, remote engine start, leather upholstery, power front seats and a removable 50/50-split third-row seat are also standard. In-car entertainment includes a navigation system, a hybrid system display and a nine-speaker Bose audio system with a CD/MP3 player, a USB port and satellite radio with real-time traffic reporting.

A sunroof and a rear-seat DVD entertainment system are the lone options.

The 2012 GMC Yukon Hybrid is available with rear-wheel or four-wheel drive. Both models utilize a 6.0-liter V8 engine coupled to a pair of 60-kilowatt electric motors located inside what GM calls an electrically variable transmission. On its own, the V8 is rated at 332 horsepower and 367 pound-feet of torque. GM engineers say that combined output with the electric motors is 379 hp.

Under light throttle/load conditions, the Yukon can accelerate up to speeds of approximately 25 mph solely on electric power, thus optimizing fuel efficiency in low-speed, stop-and-go driving conditions, while the V8's cylinder-deactivation system helps reduce fuel consumption at higher speeds. Regenerative braking replenishes the batteries by capturing energy normally lost while slowing down.

Fuel economy ratings stand at 20 mpg city/23 mpg highway and 21 mpg combined. Maximum towing capacity for a properly equipped 4WD model is 6,000 pounds.

Standard safety equipment includes front seat side airbags, full-length side curtain airbags, antilock disc brakes, traction control, OnStar and a rearview camera.

In government crash testing, the 2012 GMC Yukon Hybrid earned an overall rating of four stars (out of a possible five), with five stars for overall frontal crash protection and five stars for overall side crash protection. Its three-star rollover rating was the cause for the lower overall score.

It's not a stretch to say that driving the 2012 GMC Yukon 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 it's a tad strange, the result is a quiet cabin.

While the Hybrid is the most powerful Yukon available, it's also the heaviest, so don't expect particularly brisk acceleration. Also, the transmission can hesitate when you ask for full power. Handling is about what you'd expect: safe but ponderous. Most crossovers are notably more carlike from behind the wheel.

Aside from instrumentation, there's nothing to distinguish the Yukon Hybrid from a traditional Yukon. It boasts attractive, high-quality materials and tight panel gaps while maintaining a simple control layout. Even the standard navigation system is easy to use.

The Yukon's standard third row enables it to accommodate up to eight passengers. The 50/50-split third-row seats don't fold flat into the floor, however; they're heavy and must be removed manually to free up maximum cargo space. With the third-row seats out of the picture and the second-row seatbacks folded, cargo capacity expands to 109 cubic feet, making the Yukon the roomiest hybrid on the market.