If and When to Rebuild Transmission ('97 MC)

I have '97 Monte Carlo LS, 3.1L with 190,000+ miles that has been having what I think is transmission trouble for over 2 years. Even though I bought with a salvage title (from a close friend who told me the damage was minor) it has run great otherwise. Now I'm wanting to sell it and get something with 4 doors.

My question is would it be better to sell it as is or get the transmission rebuilt to get a better price, and how feasible would it be to try to repair it myslef. I've only done minor engine repairs which were fairly easy to figure out on my own with the help of a Hayne's manual and advice from friends. (I recently diagnosed an overheating problem as water pump failure and replaced it. I enjoyed the satisfaction of being able to do it myself.) I don't have the tools to pull an engine or anything like that, but if I thought I could do it and save money by borrowing buying the necessary tools I'd be willing to invest the time and give it a try.