Just put a 4" cat back Flow Master setup on my 2013 F150 Lariat Ecoboost. Pretty sure the one that was put on is a diesel setup. The muffler is freaking HUGE. I am not happy at all with the sound. It sounds like I am driving around a Honda Civic with a big exhaust. It also feels like I have lost some of that lower end torque. I called the shop that installed it and he is talking about putting in another muffler in line with the one that is on there that will act as a resonator. Any thoughts on this?? After reading thru some of the other threads I wish I would have left the stock on and switched out the muffler and tip. As a side note I also installed a K&N CAI.