General Motors is “exploring every technology we can to increase fuel economy,” including E85, advanced fuel management systems, diesel engines and new hybrid powertrain designs, according to Dr. Terry J. Woychowski, GM's vehicle chief engineer for full-size trucks.

In the near term, the new light-duty 2007 GMC Sierra and Chevrolet Silverado will be offered with a number of E85-capable engines that can run on ethanol, gasoline or some combination of the two.

While the 2500HD and 3500HD versions of the new truck will continue offering a Duramax diesel option, the light-duty models will not, at least for the time being.

The parallel hybrid developed two years ago for the Sierra/Silverado will not be carried forward with the new models. Instead, GM will introduce a new “two-mode hybrid” in the near future, according to Woychowski.

The new system will incorporate a transmission with two planetary gear sets, allowing it “to act like a step transmission with gears or like an infinitely variable CVT (constant velocity transmission), depending on operating conditions,” he said. For example, it would act like a standard geared transmission while accelerating, then switch to the infinitely variable mode for constant speed cruising. “That allows you to maximize fuel economy without any performance loss in truck applications,” Woychowski said.