Regulators can fail intermittently. Rare, but can happen. Put a gauge on it and exercise it by taking off the vacuum line, and returning it. Pressure should spike and then reduce. Later models work differently. They don't have a return line to the tank to circulate unused fuel. When it happens, if you can, check for spark. You have an EDIS system, and the EDIS can be tested out of the vehicle.
tom