The biggest trick with a 6.5 is to keep it from cooking itself to death.
Most 6.5 mods are geared towards improved reliability and longevity. Open up the intake/exhaust, defeat EGR if so equipped, move the FSD to a remote heat sink outside the engine bay and add gauges. Then you can think about programming/chips. (94+) Still not going to net you a whole lot, but they are fun and reliable when taken care of. If you have a 92/93 you have a mechanical pump that can be fussed with a bit.