I'm running into a similar issue with my 55' F100. Stock 223/6, stock fuel tank, lines, mechanical pump, etc. I thought at first it might have been related to the steel vac line from the distributor to the carb being loose, but it's still happening after having tightened up the vac line fittings. It's possible that it might be a heating issue as the rubber fuel line from the pump to the carb runs close to the heater hoses, and around the front of the valve cover between the breather and the upper radiator hose. Although, it has also happened at 2AM on the way home from a music gig near home......not like the hot weather on the way home from Puyallup GG show....

Having a clear float bowl cover, and a clear filter....there's plenty of fuel in the bowl, but there appears there might not be a full load of fuel in the filter...thus....it may be a failing diagphram in the mechanical fuel pump or a failing pump.....I haven't repaired/replaced it as yet, but I'm hoping that will be the issue....

Any other thoughts from the masterminds of mechanical mysteries on something I might be overlooking?