Turbo? Leaks? Recirculation valve?
Does the turbo have lots of power still or does it feel gutless (gutless could be bad turbo)? Smoking any (bad turbo, might be able to be rebuilt with factory kit)? Does the car have no power off the line and then hammer hard all of a sudden when boost is high (pressure and vacuum leaks can cause this, use a smoker at very low pressure to find them, and bump up pressure slowly as you fix the leaks)? Does it feel good but drop power at near full boost (could be bad recirculation valve, get the 71 model for cheap or go nuts and get a custom one, but the 71's are more than fine for stage 1)? Any high pitched squealing noises under boost (bad turbo, and the spindle and fins are probably running out and hitting the exhaust housing portion of the turbo)?
Have you had anyone check the car with a vagcom type setup to see if it has triggered any codes, those are extremely helpful and key in your troubleshooting. I bought the Ross-Tech vagcom adapter for $250 so I can consistently monitor my car for problems since I am keeping the car long term.
Let us know