The P30FF code is caused by a timed discrepancy between the requested boost and the actual boost. Therefore, when boost falls below what is expected/requested for a certain period of time (4th gear is a longer pull which is why many see it only in this gear), the code will be thrown.
This code is most commonly caused by a boost leak. Potential problem areas are the FMIC piping, the charge pipe, the diverter valves, or the diverter valve solenoids.
If you are sure you have no boost leaks, it might just be tired turbos that can't hold higher boost. Your Protuner could resolve this issue by lowering the load request table to match the taper you see in logs. Lower the load request to be about 10 points higher than what you can actually achieve via logging.