Check the wire from the coil (-) to the distributor. It's a good place for a frayed wire or poor connection. The wire moves constantly with the distributor under normal driving. When it heats up it breaks down, switch interrupts it and works again for a while.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine