May be a dumb question but have you checked all your manifold, turbo flange and exhaust flange bolts? Also check your bolts that secure the front and rear housing. Could be your actuator not working, where did they plumb your boost signal that was orignaly tapped into the front housing? Just trying to go through the simple things. Sounds like the turbo is trying to make the power but is possibly losing boost somewhere. Mate I agree with everyone else don't sit back and accept your car the way it is, get it tuned elsewhere. My 2c