Intermittent shutdowns are one of the toughest things to diagnose. What we are doing here is eliminating the obvious before jumping on the ECU ($$ for replacement, and they rarely go bad). So test the fuel pressure, if okay, then bypass the ballast resistor. It's windings could be breaking down when it gets hot, so bypass it and run it like that for awhile to see if it helps.
Also, it sounds like this truck is rarely driven. How old is the fuel in the tank? Throw a bottle of dry gas in the tank to get rid of any condensation that may be in the gas.