Different intake and exhaust manifolds, different exhaust system, different tuning.
The needs of a truck engine are significantly different than a car engine.
The best first steps (IMO) would be air intake, exhaust system and tuner. The intake and exhaust alone might show slight gains in HP and MPG, but they allow the engine to breathe better. Adding a good tune will work with them to give you a noticeable increase. Many of the "canned" tunes included with the tuner will give you a good starting point, and may be all you need.