My advice when buying a used vehicle, especially one that's almost 20 years old:
You MUST take it to a mechanic. Definitely don't let them pick the mechanic either. Finding a referral for a good mechanic might be hard to do, may want to take it to their local Jeep dealer and have them look at it. Any vehicle that old will likely need some work.
I like to watch People's Court. Everyone that buys a used lemon gets yelled at by the judge: 'WHY DIDN'T YOU TAKE IT TO A MECHANIC!!!'
I agree with the above: a rebuilt tranny is better than a worn out one that hasn't been rebuilt. If they did it right, that's another story.