1991 Chevrolet S10 pickup truck

I recently bought this from a friend who is moving... It was his daily driver until the transmission quit working... I have an estimate to get it rebuilt for around $700 ... It may not need rebuilding ...I’m not a transmission guy so I do not know. The truck is driveable if it’s cold... I drove it home to my house. Once it gets hot it will not move... It’s like it’s in neutral . It will need to be trailered away because it just stops moving once it gets warm within 3 minutes... It may be a simple fix, I’m not sure but my loss,YOUR GAIN. Odometer shows 270k but not actual... Motor has been rebuilt. The Good- was recently inspected- good until 09/2018 Has the bulletproof 4.3 engine that runs excellent...has been rebuilt Has newer exhaust and tires. Has newer air conditioning that works. The bad- the heater hoses to the heater coil have been disconnected from the radiator ... The radiator has 2 plugs where the 2 hoses went to it for the heater coil. Maybe the heater coil was leaking so it was disconnected ...I don’t know Truck comes with 2 newer bucket seats, has a bench seat now. Also includes 2 front fenders as spares. This would be an excellent first car or hunting truck... Odometer shows 270,000 on the body but motor has been rebuilt...