Intake and exhaust, not necessarily in that order. the biggest gain I had before the computer was the exhaust. and removing restrictions from the intake.. after that when my power steering pump exploded (yes exploded long story) I yanked it to replace it and discovered that the truck gained all sorts of pep, so i never replaced it.

above all this all I can say is what I tell everyone, CLEAN your throttle body and do a good solid tune-up then start the mods..