I am considering putting gibson headers on my 04 5.4, I already have Superchip max micro, Airaid, and 1 in 2 out flowmaster dumping before the rear axle. Does anyone have headers and can you feel any gains. They are around 400$ but it might be worth it for 15hp.

 

Do a search here and on the aftermarket exhaust board. Our stock manifolds flow extremely well. It has been proven that you won't gain much, if anything, with shorties.