you say; "if it were a fuel issue it would not fire back up", that is not actually correct. an almost 'all the way full of garbage' fuel filter or clogged 'last chance screen' sometimes will allow enough fuel to fire off, but not enough fuel sustained to allow it to run [often shows up in a "stalls in a tight turn while driving 'at speed'."], and that is often how the symptom first appears, that the truck dies while running but will restart, but a lot of operators will keep on using and restarting until it gets so that it runs for only a short period, then they call the tech.
BUT,,, since you are feeling like it is a safety shutdown, have you confirmed the working of the temp sending units? does it have oil in the motor and does the low oil shutdown circuit work? is power getting to the pump 'run/shutdown solenoid' wile running and not just while cranking?