Quote Originally Posted by Andrew_99GTP View Post
Dang maybe I will have to reconsider getting one for the GS and get one for the trubo gp. Maybe it will increase exhaust gas velocity if I put it before the turbo?

I really don't know alot about turbos so I cannot help you there. I would check your muffler bearings. Most likely they are getting wore out which would hurt your mileage a bit. Throw some new bearings and an O pipe on there and you should see a 3-4 MPG difference. If you have bad bearings it really slows down your exhaust flow and just kills mileage. These 2 things will only cost you $150 and will make a big difference.