another exhaust question....
im tryin to get new headers and high flow cats as cheap as possible
would it be better to swap a 2.5'' pipe with my stock 2.25'' pipe before the muffler or not?

 

have you seen what's entailed in doing the headers? I just looked at doing a set on my 2005 5.4L last weekend while it was up in the air....I can tell you that unless I crack a manifold then it's never happening. You might be better off putting the money into another mod.

As for the exhaust, I'd go for dual 2.5" pipes into a dual in/dual out magnaflow muffler. Look into having it done custom - should run about the same as a kit but with a better fit.