1988 Other Chevrolet Models Motor Home acts like it running

I bought a Motor Home that has been sitting for 4 years maybe more. I drove it home from Pittsburg, aout 4 hours, and it worked fine. I drove back and forth to a shop for service 2 times, about an hour. I was taking it the shop and it started acting like it was running out of gas. I was patting the gas pedal and kept the hard acceleration off the engin it ran and probally would have kept running. I assumed it was out of and gas and pulled over to keep from running the line dry and or pulling who knows what out of the tank. It sat for about 1/2 an hour or so by the time I got back and installed gas. I got in and it started right up and ran fine. I assumed again that it was out of gas and stopped and put gas in it. It started and ran for a mile or so and statred doing the same thing, acting like it was out of gas. I babied it to the shop. They drove it around the building and it did not act up. I took it and was driving it and a few miles down the road it started having the same problems/symptoms. When the engin is cool it appears to run fine, as it gets warm is when it starts to act up.
I had the filter at the carb replaced, the fuel pump, plugs, wires, dist cap replaced and it still does it.
What would be the next thing to look for? Or get replaced?