I had the same indications - except I was smoking down the back stretch at Mid Ohio at the time. Needless to say, it got my attention. It was a good thing I was wearing a full harness. I had a Porsche certified tech at the track look at it and he couldn't determine the cause. But he suspected a vacuum leak. Like Diskzero, I replaced all of the vacuum lines (with the kit from Lindsey Racing) and installed a new Blow Off Valve - problem solved.

Chip

 

"Danno, do the GURU chips still retain overboost protection??"

The overboost is triggered based on values in an RPM-based table. I reprogram that in the DME to raise the overboost protection as high as possible. Also remove it from the KLR as well, although that's not as important since most of the time, you've bypassed the KLR with a manual controller anyway. I'm not sure if the KLR messes with the timing in any way when it detects overboost (CPU code is read-protected), but safe bet to replace the KLR chip anyway.