it could also be your high flow cat. When the cat starts to break down it causes a block in your air flow and the enginge runs like crap hence getting the breaking feeling this is what happened to my honda when my cat went bad. I would have the cat checked and make sure the guys who sold it to you aren't getting on over on you. Tuning for a cat is stupid. The only thing that needs to happen is the car needs to be driven about 50 miles for the ECU to refigure itself. But still that wouldn't cause the braking affect. My bet is you got a bad cat.