are you sure its ur exhaust like did it happen right after it, and also another thing to think about if u do or not cause i know i did that made my gas mileage suck till i realized i was doing it is when u get a new exhaust its louder so u might have the tendencie to hit the gas more or accel harder or stay in it longer so hints ur gas mileage goes down lol but all in all i put on custom true dual 3inch striaght pipe on my 2000 and didnt effect gas mileage minus me making it effect it