forcedbird

My car is a 00' m6 firebird. I took the father-in-law out for a ride today. Car ran fine, I noticed though, the boost guage only showing about 5.5 pounds. I normally see about 2+ more. I had my car an open lap road course event last weekend. I'm wondering if the on and off loading of the blower and engine could have stretched the belt and now it is slipping? I do have some "black dust" around the pulley but I've gotten some of this since the blower was installed over a year ago. I checked all of the connections and the balancer bolt and pulley are all tight. Do you think that the by-pass valve could be the culprit? Should I just replace the belt?

thanx