What engine is that? 8.1 Vortec 496 rated at 450 horse power? When were your spark plugs last replaced? Maybe the map sensor. It is simple to replace and runs about $65 bucks at the auto part store. That is where I would start and see if there is any improvement. If not then you may be looking at an injector problem. But that's where I would start. I am looking at getting a Scanner for my engine so that I can do more diagnosis.