1993 Nissan Truck What to do and is it worth it.

Hi, great website! We know little about cars, but do know in its current condition our '93 Nissan pickup is probably only worth $1100-$1600.

THE PROBLEM: While driving and without a sound or warning, it suddenly coasted to a stop (no drive or reverse) but the engine continued to run (like it had been kicked into neutral). We're thinking maybe transmission? Transmission fluid is full.

OUR QUESTIONS: What might be wrong and, though we know it's up to us and hard to say, would it seem likely to try to find out given the value of the truck or just sell it off? Thanks!