I am having this EXACT same problem right now. Does it also make a different sound when it hits that point and loses power? Mine also only does it some of the time. Right when I start the car and it just barely has warmed up it will boost hard all the way thru the RPM's, but after driving it for awhile if I push it hard power cuts out. Also it is worse in first and second gear, and as time goes on third goes then 4th then eventually 5th. Extremely annoying issue. I've been pondering injectors, boost leaks, or some kind of electrical issue, but it SOUNDS like a physical problem. I am also getting a boost controller/gauge to monitor and also control boost more accurately to see if my boost jets are causing the problem.
15:10:13 07/14/11
