The Contenders Our truck of choice: a 5,879-pound Chevy Silverado LS 2500HD Crew Cab with a 6.6-liter turbodiesel V8 (diesels typically get better mileage). Trucks, sport-utes included, are subject to more aerodynamic drag because of their large front area and high ride height. To counter, we set the Chevy's cruise control at 55 mph for the duration. Also, on the advice of GM's Roger Clark, we altered the truck (see left) to improve mileage. The EPA doesn't test heavy-duty trucks, but GM's internal testing indicates 17 mpg on the highway.