To expand on Bartamos' comment, I had a '72 Chevy PU that would cut out on the road at random times. I wound up replacing the resistance wire from the ignition switch to the coil and it STILL did it.
The fix was (eventually) taking the terminals out of the clip that connects the wires to the coil and squeezing them a bit more shut with a pair of pliers. It was losing continuity because the connection was loose.
Worked just fine after that till I sold that truck. Sometimes the easy fix is hard to find.
