Couple of questions - 1) has the FI light come on? 2) Does the behavior happen at a particular speed or a particular rpm?
I had the same trouble but it happened if I held the RPM constant at 3-4 Krpm... in my case they replaced the throttle sensor under warranty (took 3-4 days to source the part, costs about 15-18K). I'd suggest you get the PBK guys to sort it out soon and use the warranty...
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