To big of an exhaust?
 

Ok I just put a megan racing turbo type cat-back with 3 inch pipeing on my 97 gs-t. Its the only thing aftermarket on the car and I needed a 3 inch flang to make it fit on the stock cat. The problem is say Im doing about 55 and I try to go faster my rpms will start at about 2.5k and stay there or it might go up to 3k and kind of drop off. The car is an automatic too. I never noticed it do that befor I put the cat-back on, so what is the problem and how can I fix it?

RE: To big of an exhaust?
 

well that exhaust definetly isnt too big. So that is not your problem...do you have an exhaust leak? Are all the new gaskets good and installed correctly. That is where i would start since your saying its only started now.

RE: To big of an exhaust?
 

the 3 inch piping is not too big, your problem lies elsewhere in your exhaust, check all your seals.