I have a 04 F150 FX4 with the 5.4l, im going to order a super 44 flowmaster, and have a shop build my exhaust for me in town here. Now if im not mistaken, the stock exhaust on my truck is 3in before the muffler and 2.5 after the muffler right?? And i also want to know should i go with a 3in si/ 3in do, or a 3in si/ 2.5 do?? Thanks much.