Yea it was chipped before de-catting it. It does feel like theres not enough back pressure.
The exhaust is blowing, so yesterday I had a good look at it and it's A1. I've had a quick check at the manifold but theres no visible cracks or anything. Could it possibly be the manifold blowing thats causing the problems? It's hard to get to the back of it without having it up on the ramp.
Thanks for the reply