I'm not sure there is much you can do. I've never seen a hotter ECM for a TBI truck. There is probably a custom tune shop somewhere. Maybe a Shelby Dak ECM would work if you could find it.

Dual exhaust, K & N air filter, good plugs, wires, cap, and rotor, pretty standard easy upgrades.

Is it a 318 or 360? How many miles?

What are you looking to do with it, mud bog, street race? Personally, I've always felt power is in the heads and cam. How much do you want to spend?