It's a GTP, which means that even if you're not beating on it, there's a decent chance the previous owner(s) did. Anytime you're dealing with forced induction, you're going to have higher maintenance costs because the engine endures much higher stresses than a typical n/a engine.

I think you need to find someone that can hook an aeroforce or tuning laptop up to your car, then hit the highway and reproduce the problem with the scanners on it. That'll tell you what is causing the issue.