Engine dies without warning

1992 GMC 1500 truck, manual transmission, with 35000 miles. Doesn’t get much use - 5,000 miles in last 5 years. Used mostly for Home Depot runs and camping with the grandkids. Twice in the last 3 months the engine has died without warning - no lugging of engine, no warning lights - while traveling 70 mpg on highway. Starts right up again. In between the two incidents I drove it 500 miles between San Francisco and San Diego and another 100 miles between San Diego and Pomona. The mechanics at the local shop could not duplicate the condition, nor could they find anything wrong that they might cause the problem. Help! I don’t want to drive a truck that might quit on me on the highway!

Seldom used vehicles accumulate problems.

When was the last time the fuel filter was replaced?

If not a fuel supply fault then it’s going to be an electrical one. Perhaps an ignition problem.

Being an intermittent fault, this MAY take some time to track down.

I can understand your concern about the engine shutting down without any warning.
Until the fault has been located and repaired you MAY want to think about slowing down for safety’s sake.

If it starts right up you may never find out but I would buy one of these. If it does not start right up put this between plug and plug wire then you will know if it is fuel or spark.