Hi, had a 454 for 14 years. Seen it all. Had simular prob. The old coach had settled down lower on the chassis. This allowed the fuel hoses atop the tank to rub on them until small holes developed. When pulling long gradual grades over time air was slowly sucked thru these holes. Engine would act like your's. Pull over, the line suction would be reduced and it sucked fuel again. Another possible...there are two electronic modules in the distributor. They get hot and begin to fail with your symptoms. Replace em.
