Ok, here it is:
Glad I could help. Sounds to me like your BCS isn't hooked up properly or isn't working properly. You should have a vacuum line running from the wastegate actuator to a tee. One side of the tee goes to the turbo or piping very close to it, and the other side goes to the BCS. On the other side of the BCS, there should be a line plumbed back into the intake tube, pre-turbo. Make sure the wiring to the BCS is plugged in and looks ok. Read this link and take a look at the pic. The BCS is the wastegate solenoid valve.
Boost Control FAQ: Read if you are thinking of buying one! - NASIOC
This next thread has some useful pics showing locations in the engine bay, but the thread is about installing a GM BCS as a mod.
Full DIY: GM solenoid install (56k warning) - NASIOC