I have searched for vacuum leaks and currently have the vacuum port that goes to my AC controls connected to a vacuum gauge and the vacuum that controls the EGR is pinched off. My exhaust system is 2 inch duals with a crossover pipe in between them and 2 40 series flowmasters. I actually stuffed a rag in one side just to see if backpressure made a difference. It's just a guess but I would say that this truck as little to no backpressure because of the exhaust system, at least at idle speeds. Maybe this is a problem I have created