My '92 truck has the 4-spd auto, and I'm quite happy with it overall. If I was doing serious towing of over 10,000 pounds, that might be a different story. If the transmission has received regular maintenance, in my opinion it should last at least 150k. Mine has 145k, so I'm running Amsoil synthetic ATF and keeping my fingers crossed, but so far it's fine. The only problem mine has is with torque converter drainback in the morning, but a few seconds of fast idling in neutral cures that.
Assuming the truck is a Wisconsin native, I'd be looking close at the body & frame rust situation, especially that frame rail adjacent to the fuel tank. That's a nasty spot for salt to collect, and I have to keep flushing the frame on mine in the winter to keep it rust-free.
Best wishes.
- Mike