[fred]

Points or electronic ignition? My guess is that it's heat related which points to a distributer problem (hey I made a punny!) On a Motorhome it's an outside chance, but you may want to check for a clogged cat/muffler. It's a little difficult, but check to see if there is fuel in the carb (accelerator pump/ dripping into the venturi's. . Quite possibly the ignition module. (I was a young man till I ran into Dodge motorhomes).