Custom programming tends to enhance other mods. The first things most people start with are:
(1) Air intake (Mac, K&N, Volant, KKM etc)to replace restrictive OEM airbox (allows engine to inhale better)
(2) Free flowing exhaust (Flowmaster, Magnaflow, Mac, Gibson, Flo Pro etc) from the cats back ("catback", allows engine to exhale better)
(3) Custom programming via chip or flasher (bamachips etc), better shift points etc.
Search the heck out of these forums. The site's been in existence for years and the questions you want addressed have probably been addressed zillions of times in the archives. Custom programming in isolation doesn't do much. It more or less ties in the other mods. Doug (bamachips) takes the specifics of your vehicle (including mods) and furnishes programs accordingly. The delivery mechanism is via chip or flasher. I've used both and definitely prefer flasher method. Way more flexibility and much easier to deal with. Ask about the XCalibrator2 flasher.