Nothing wrong with the factory mouth piece on a stock truck. In my opinion it's not even really beneficial or worth the money on a stock trans- safe tuned truck.
But when you are running a max effort tune with the stock turbo it is a restriction
Maybe my butt dyno needs an adjustment :rofl:
I really didn't feel a difference in trucks I've driven with and without. Haven't installed one on mine yet so I can't vouch for my personal truck. Comparing before and after on a truck I installed one on I didn't notice a real difference. It was stock trans tuned by ppei I believe. Others I've driven with them and compared to my factory mouthpiece truck didn't feel any more responsive down low.
Maybe I'm not observant enough, to each his own.