1988 Ford F 250 F250 Pickup 4x4 Which Between Our Biological Field Station Town

I have a Ford F250 pickup 4x4 which we use to go between our biological field station and town here in Bocas del Toro, Panama. The vehicle starts fine when cold, but will suddenly die while driving to town, and then will not start again until 24 hrs has passed. Each time, I was about half way between town and the station, or about five miles out. It doesn’t hesitate or die slowly (like running out of gas), it just dies all at once as though someone turned off the switch. I have had the carburetor, fuel line, filter cleaned and the wires checked but the problem persists. What could cause this? The vehicle has over 300k miles on it but otherwise was running fine.

Peter