When I'm driving my BF MKII with its generic flash tune and the boost starts getting up over 5psi it splutters and loses power until I take the foot off the pedal. It only really does it in 3rd,4th,5th, and 6th gears. When I flash it back to stock its fine just the higher boost is causing issues. The boost stays stable while its shuddering it doesnt spike or anything it seems to hold boost. Fraud checked it out but I flashed it back to stock so they couldn't really tell. Any help would be greatly appreciated.