He had the black painted ones on a 4x2 but yea could be a factory defect as well, I heard it's a bit tighter on a 2wd. If the 3" with an H pipe is too much flow then I'd think he'd be fine with an X pipe or just go 2.5" it's all up to you and I know you lose a lot of nice sound with y-pipes.
I was looking at this for when I go to redo my own exhaust:
OBX HEADER EXHAUST MANIFOLD 04-08 FORD F150 F-150 4WD | eBay
$570 and it's all ss I was just going to get someone to tig an x-pipe on it. Seen a few good responses on them also.
I think it's $170 more for cats instead of resonators or get a custom tune it's a bit more but, it'll never rust.
OBX HEADER CAT'D 04-08 F150 F-150 5.4L 4WD 4X4 Manifold