[Ski-me]

Thanks Keith for a new website! Wasn't aware of that one.

To OP, I think you have a lot of deferred maintenance that needs to be done.
Change Oils (engine, axles, tranny), do a tune up, clean up any obvious wiring issues (bad splices), check and service brakes. With axle fluid change, replace rear seals too at same time. Front is a little more involved.....

You need a good base to get an idea how the truck will perform.

Exhaust leaks, can contribute to power loss a bit, but not huge (relatively speaking).
Low oil isn't going to contribute to power loss either. Just maintenance.

These are not power demons compared to today's modern vehicles but they are still a lot of fun! I have 360k on my 89' and it is very reliable. I drive it almost every day and 2 of my 3 girls have learned to drive on it.

If it's lacking rust, you have a very decent rig!