Well, after numerous hours clicking sound clips and researching different mufflers online, I finally upgraded my 03 supercrew exhaust. I didn't want to spend an arm and a leg, and was more concerned with improving the pathetic sound of the stock 4.6. Heres what I did, I stuck with the factory 2.5 inch piping, and had an original 40 series flow put on with a 3.5 inch tip. I was apprehensive about putting the flow on, but to my surprize, it's awesome.

Sound details

low deep rumble at idle
deep mellow acceleration
deep aggresive tone on hard acceleration
no in cabin drone at any cruising speed
highway cruising is virtually silent

I was worried about the sound quality, but I couldn't be happier with it so, if you want your 4.6 to sound it's best go with the 40 flow on stock pipes, I had the whole thing, parts(muffler and tip) labor for 103 dollars, and if you live in the pensacola area I can tell you where this amazing deal can be had.