I hope you find out cause im having the same problem as well, I have changed plugs and fuel filter next will be fuel pump, I can drive through every gear smoothly but as soon as I put the foot down and it hits boost it shutters like its on the limiter. hopefully someone else is having the problem and has fixed it, I have been told by an ex performance guy that this is a common problem in them and to replace fuel pump with a bosch 044 fuel pump, fingers crossed it works, will let you know how I goin the next couple of days
