DETROIT — General Motors delivered 50 full-size extended cab hybrid pickups to Miami-Dade County fleet in Florida. GM made the first delivery of the 50 Chevrolet Silverado pickups at the 10th National Clean Cities Conference and Expo in Fort Lauderdale, Fla. The trucks feature a V-8 engine and four-speed automatic transmission coupled with hybrid technology that delivers 10- to 12-percent improved fuel economy over GM’s conventional half-ton pickups. The Silverado is considered a “mild” hybrid. Hybrids draw power from two energy sources, typically a gas or diesel engine combined with an electric motor. In addition to improvements in fuel economy and emissions, GM’s first hybrid pickups — the Silverado as well as the GMC Sierra — feature four 120-volt, 20-amp electrical auxiliary power outlets under the rear seat of the cab and in the pickup bed.