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.
1995 Bonneville SSEi:
(still without a motor and tranny) 15.606 @ 87.95mph (stock)
1998 Regal GS:
DHP 1.0, JMB FWI, ZZP 3" DP, 04 GP 12" Brakes, ZZP 180° Drilled T-Stat, SLP Single Outlet Catback, Silverstars