Have seen the distributers get bad on those, but there must be some kind of secondary ignition problem. Try and use a spray bottle while it's running, and see what may cause it to stall. Wires, distributer, coil, etc.
I would agree with previous answer, but also test for possible failure of the Ignition module... This would attribute to a spark or ignition condition supported by the starting fluid failing to start the engine.
ICM's or ignition control module's are common to fail when hot and will work when cooled.
4.3L also have a common issue relating to the coolant temp sensor, when they heat up they can have voltage issues causing the PCM send false commands to fuel system. I've seen engines get overload of fuel, causing massive flooding and also seen them cause a no fuel issue. Smell for excessive gas smells during a no run condition. Or next time it acts up you can unplug the Coolant Temp Sensor to see if it changes. May cause a DTC or Check Engine Light, but this may be cleared by unhooking ground on battery for a few min in the year of your truck.
