Chevy introduced its 2009 Silverado hybrid truck at the 2007 Los Angeles Auto Show, using the green state to show us the green truck. The Silverado is controlled by GM's 2-Mode hybrid system, which includes a transmission that can vary its gear ratios in infinite ways -- or operate as a conventional tranny with four fixed gears when the truck is running at high speeds or carrying a load.
The Silverado hybrid is available as a Crew Cab in either a 2WD or 4WD configuration. Expect to see it on dealer lots in late 2008. (Update: Silverado Hybrids won't be available until 2009)
More About the 2009 Silverado Hybrid Truck
First Drive: Silverado and Sierra Hybrid Trucks

