Why is my new 2010 Silverado 3500HD 4x4 Ext cab long box SRW, 6.0 ltr, auto, 4:10 ratio truck with variable valve timing such a dog? Previous 6.0's halled butt. This truck can't figure out what gear to be in, and has to down shift 3 gears to get to 5,000 rpm to do anything. Truck has no low end torque. Dealer says it's functioning as designed. GM please fix this thing or I am changing my fleet to Ford.