If it's the BPC as all you guys suggest, then why isn't it failing for the stock program as well? Seems to me like if it was stuck one way or the other (i.e. stuck open and you're only getting base boost or stuck shut and you're getting uncontrolled boost) it would be stuck no matter what chip was in there.
What psi is the fuel cutoff? That's what it sounds like to me too but I can't imagine why the chip would be letting you hit it.
Do you have a real boost gauge or just the one in the dash?
And sorry about my comment earlier.
I should have assumed that you'd think of that!