We had this problem last year - took the coach to the Onan-Cummins dealer and they played with it for a week and couldn't replicate the problem. I had them do a full oil change (since we were there and all) and it's worked fine ever since. When I was doing my research, there was a lot of speculation about the fuel filter getting clogged as we were driving - but never got anything definitive.
Kinda frustrating, but it works now so okay......
2015 Georgetown 351DS
Chris, Garren (humans)
Edgar & Carlos (felines)
RIP Sophie, the sweetest cat ever.