I have a Silverado 2500HD with a 6.0 L (gas). When I drive the truck under under a load like going up a hill on the highway or try to tow my camper I have no power to keep the truck going above 55 (Loaded or unloaded). HELP!!!! Just put a new tranny in about 1000 miles, fuel filter, plugs, wires.

Welcome to AF. Misfires, holds backs, slows down, need better explanation of no power.