with the exhaust... trial and error pretty much...
if i had 2K.... i'd go with the underdrive pulleys, electric fan, port and polished TB, then work the gears. i'd personnaly go with 4.11 gears. or if you can get an R/T rear, they came with the 3.92 gears.
TB- $80 (look up bwdakrt)
underdrive pulleys - not totally sure on price (lookup Deanler, link in his sig)
electris fan - local junkyard. you can get one from 01-04 dakotas... i believe thats the years for them
R/T rear - $~800 from a junkyard. (at least around my way anyway)
4.10 / 4.11 gears - assuming you have the 8.25 rear (10 bolt) (look here >
NATIONAL DRIVETRAIN: Differential, Drivetrain & Ring and Pinion Supersite )