The 3rd gen(89-95) transmissions if serviced regularly should last several 100k, like the engine. If you want to get a good listen to the tranny w/o road or driveline noise, turn the engine on and leave the E-brake on, then shift the T-case in neutral, you can then accelerate the engine and shift through the gears while sitting still. You will be able to hear if the tranny is bad.

When you say the radiator fluid came gushing out did it spray out or just bubble out? When it is a warm or hot day mine will sometimes do that even when the engine is cold.

Depending on the asking price even if the tranny needs to be rebuilt and the HG replaced it could be a good buy. Here in CA it would sell for around $2k for a stock rig needing an HG and tranny rebuild, providing the rest of the rig was clean.