what exactly is the difference between 99-00 and 01-04 ??

i thought it was just 90 mass air and the 3.73 gears.... that makes 20hp???? or is there something else?

 

It's the lower intake design. For 01, Ford added in sections of intake runner before the ports on the heads instead of it just being a big open plenumn. That's where the gains come from.

 

performance wise yeah thats about it with the exception that ford cut a little larger hole in the fender for more air. also a aluminum drive shaft too but big whoopie.

The big thing was the computer programing that ford changed for a little more performance, thats where most of the power came from. The 90 MM didn't help that much stock but makes a big diff when your trying to ram more air in there like we are now.

cosmetically they changed allot of interior stuff over the years and wheels and suspension and what not.