Hey Tom, it sounds like you have an issue with the wastegate. Inspect all the vacuum hoses that attach to the turbo and make sure they are in good condition. It is also probably worth a try to clean or replace the stock BCS (Boost Control Solenoid). They can get a bit gunked up in the solenoid and then no longer function. You can clean the thing down with some carb cleaner and see if it will work, or replacement. Someone may have one local that you could try and see if that is the problem. The BCS takes only a few minutes to swap.
Best of luck.