Those of us trying to keep em' running in the 70's saw a bunch of this "sometimes pluggage" on the vahicles of the late 60's-early 70's---mostly GM.
Many times the vehicle would run normally for days and then shutdown on the road only to restart after a short rest.
Sometimes you could make it repeat by making a high speed or load effort like open throttle uphill.
I never found out what had changed in the way the vehicle was made from earlier or later but the plastic gauze type filter on the pickup was at fault and sometimes left a imprint where it was sucked up against the pickup tube.After the suction was interrupted it backed off and buisness as usual.
Sometimes mechanics would blow back with air to clear the situation but the real cure was replacement of the pickup assembly or rip off the filter and install a good inline.
