I definatly agree with Chevyguy 100% about a chip. Thats one of the things TBI has going for it, is the computer. You might find out that you need to get better gears, 3.42's just aint enough for towing. 3.73's would be a much bigger help.
A good RV cam will help out too. But if your going to tear into the engine, might as well rebuild it.
Boring an engine your-self, could prove to be not a very good idea, ive though of it myself, certainly save a few HUNDRED bucks! If ya got a spare block lying around go for it! and let us know how ya do, and what ya did.
before you start adding performance parts, you need to consider your budget, and how many miles are the current motor. 100,000, id go down the list, 150,000 getting close to rebuild time. But here is a list of what I consider to be most benificial in order of what I would do (key word being I)
1) Tune up ( AC/Delco plugs, MSD or Moroso wires, MSD or Moroso Cap and rotor kit.) the obvious.
2) Throttle body spacer
3) Gears, deffinatly if ya got anything less then 3.73's
4) Exhaust (Headers, and a much more free flowing exhaust all the way back. Check out some of the kits from flowmaster)
5) Chip, now that you can move more exhaust with a good exhaust system.
6) I'd get some kind of better flowing intake system like a K&N kit.
7) Edelbrock sells an intake manifold for TBI systems, this is a very good option.
an Updated ignition system is a must Check out the MSD 6 series systems in summit, (If you do decide to run an MSD ignition system, Gotta run MSD wires with it.)
9) if you still dont have enough power, try some March aluminum pulleys (in summit.)
10) If you still aint got enough, you can always switch to a carb set up with Edelbrock intake.
11) finally if all that just aint enough. Its time for a rebuild.
Well I hope this helps out, Good luck!