help please??

hey guys im in serious need of some help with my car, its really running like crap, im only gettin about half the boost that i normally do, i cant even chirp the tires off the line. Does anybody have any clue what it could be, if so please let me know asap. I have flushed the tranny, changed the oil, new plugs and wires, fuel filter, oil filter, air filter, pretty much everything i can think of but nothing seems to be helping. Is it possible that i have to rebuild my s/c?? Any help would be nice thank.

Is your GTP stock and how many miles? What condition is the SC drive belt and pulley in? Any abnormal noises from under the hood? Do you still have the original coupler that connects the snout to the main body drive gearing? Also, make sure the vacuum lines are good around the boost valve and the boost valve is working properly.

its completely stock with 117000 miles and the s/c and belts are in good condition, and there are no wierd sounds, and i really dont kno enough about my engine yet to know anything about that other stuff