GM says the Sierra Hybrid's gasoline V-8 and electric motors team up for an overall mileage improvement of 25 percent. Its only direct competitor is its corporate sibling, the Chevrolet Silverado Hybrid. The Sierra Hybrid goes on sale in late 2008 as a rear- or four-wheel-drive crew cab, both with a 6.0-liter V-8 and two electric transmission motors. Standard features that are optional on the regular Sierra include an electronic stability system, a trailering package, locking rear differential and side curtain airbags.
Alongside the Sierra Hybrid's lower panels are green stripes with "hybrid" in capital letters. There's also hybrid badging on the cab's rear window, ahead of the side mirrors and on the tailgate.
Eighteen-inch alloy wheels wear low-rolling-resistance tires, and the front air dam is slightly deeper to reduce wind resistance. The changes don't look as dramatic as they are for the Chevrolet Tahoe and GMC Yukon hybrids, both of which share drivetrains with the Sierra Hybrid.
The Sierra Hybrid adopts the boxier of the Sierra's two available interiors, with a flat cowl that spans the gauges and center controls. Available features include dual-zone automatic climate control, leather seats and a navigation system.
The hybrid drivetrain's battery pack sits under the rear seat. Like in many hybrids, the navigation system has a screen that displays the flow of power between the engine, electric motor and wheels.
Under the Hood
GM's two-mode hybrid system enables "full" hybrid operation with the capability to cruise on electric power at up to 30 mph. The gas engine kicks in if more acceleration is needed, as well as at higher speeds; for maximum grunt, the electric motors and gas engine work together.
At the heart of the Sierra Hybrid is a 6.0-liter V-8 that teams with GM's Electrically Variable Transmission, which integrates two 60-kilowatt electric motors. The motors draw power from a 300-volt battery pack, which recharges itself off the friction generated when you hit the brakes. The engine makes 332 horsepower and enables a towing capacity of 6,100 pounds with rear-wheel drive and 5,900 pounds with four-wheel drive — not as much as the regular Sierra's 10,500-pound maximum towing capacity, but not too shabby for a hybrid.
GM says gas mileage is up 40 percent in the city and 25 percent overall versus the gasoline Sierra.
Four-wheel-disc antilock brakes, traction control and an electronic stability system are standard, as are side curtain airbags for both rows of seats.