Ok stg313, i gues that narrows it down to my stock muffler. I'm guessing it can't handle the mass air flow from the headers & when it shifts the let off is creating a back flow through the baffles in the muffler or something. I need to change out the muffler anyway to get best flow, i just didn't want the exhaust to be real loud. Hey what a difference a air intake, headers and a tune make huh!