2 mods that I have done so far to my '03 DC are the 4" deck plate mod and flex-a-lite 675 electric fan. Next will be TRD headers and exhaust.

Biggest bang for your buck is the deckplate mod. Dynos @ avg. (6hp) for a 100$CDN.
Deck Plate Mod

Flex-a-lite install and review coming soon.