Major tuneup. Seriously. Nnot just plugs & wires. Replace ALL fluids, diffs, t-case etc, valve adjustment. Download the FSM, and go from one end of the engine to the other checking everything you can, and replace / clean / repair everything that fails the tests the FSM lays out. It'll take you all day, but a maintained engine is a happy engine.
Then, and only then, look into bolt on go-fast parts. Cat back exhaust is the biggest bang for the buck (2 1/4" is most popular) - consider asking a local muffler shop for a used / clean V6 muffler (people frequently take their brand new car straight to the muffler shop & get new pipes). Do a search for "Snorkel" for a cheap CAI. Header is good, but a bit of a diminishing return - I'd do a re-ground cam first (1/2 the price).