There are lots of little differences on the 99-04 models, there are the more major visible changes in the 99-00 vs 01-up (hood scoop, side scoop, improved cup holders, and double DIN stereo slot instead of a pair of single DIN slots) On the mechanical side there were some minor changes each year, plus the major change of the Windsor block being used in the 99 & 00 vs. the Romeo in the 01+. Some of the other more minor changes are, the water pump (different underdrive pullies), different manual transmission T45-T3650 mid year 01, change of MAF design to integrate IAT with MAF in 03 I think, change of tensioner/belt routing in 00 or 01, etc. There are several minor cosmetic changes over the years, seat back pockets, A/C vents, etc.