At first glance, the 2011 Chevrolet Heavy Duty trucks haven't changed much. The Silverado 2500 I drove for a week looked very much the same as last year's model on the outside and retains the 6.6-liter diesel motor and the Allison transmission.

However, I found that the trucks have hundreds of invisible changes! First, under the hood, horsepower and torque are up dramatically. Last year's ratings were 365 hp and 660 lbs. of torque. This year's ratings are 397 hp and 765 lbs. of torque.