I have the same problem described initally, my boost gauge only goes to 0 or +1 EXCEPT if it is raining or moist conditions out. Got me stumped. What vaccuum did you replace\repair? My supercharger will go up to 7 if it is very humid or rainy out.

do you get the check engine light comming on too?

no the light is not and does not come on

I would first check for any vaccum leaks under the supercharger cover. Might have a cracked or disconnected vaccum hose and if not, you might have the same problem as i had and the boost bypass sylenoid is bad. But to do a check to find out if the boost bypass sylenoid is bad, do the boost bypass that some of the guys have done. If you do this and boost goes back up to where it should be at WOT then the boost bypass sylenoid is bad and its not really an expensive item. Its like $14 on www.gmpartsdirect.com You can search for the boost bypass here under forced induction. Hope this helps.