My reccomended list:
Gears (3.73, 4.10, or 3.55 if it's going to be on the highway a lot)
Exaust (Headers [I like longtubes], H or X Pipe, and a "catback" [Flowmaster, Borla, Bassani, Magnaflow, etc.]
Electric fan
Shifter (shift kit for an automatic?)
If you want all motor power...