Welcome and thank you for allowing me to assist you! This sounds to me like a fuel delivery problem. You did not mention replacing the fuel filter in your question. Did you replace it?
Ok Cass, just be sure they did because a plugged up fuel filter will cause the exact same issue you are experiencing. If they did replace the fuel filter, then you may still have a plugged up fuel pick up screen inside of the tank, or a plugged vent in the gas cap. I think that something is preventing enough fuel volume from getting to the fuel pump and carburetor. One way to check for adequate fuel flow is to remove the supply line from the tank at the pump. Fuel should easily flow out of the disconnected line. If it does not, then suspect a plugged fuel filter, plugged screen in the tank, or a tank venting problem.
I hope this information helps, and let me know if you need further assistance with this.
Sorry Cass I had to step away from my computer for a bit. I see that you have 7.5 lbs of fuel pressure at the carb. Can you leave your test gauge tee'd into the fuel line at the carb and then drive the motor home and watch the pressure when it starts to act up? If it holds at 7.5 lbs, then I will be satisfied with fuel delivery to the carb. If it drops off, then my theory of a fuel delivery still stands. If it is not a fuel delivery issue, then it would have to be a weak spark or maybe a plugged exhaust problem. Try to check the fuel pressure while driving and let me know,
That is awesome Cass! It just really sounded like a poor fuel flow issue and glad that it was only a fuel filter. By the way the "numbskull" reference is right on. I cannot believe that it was not replaced.
Glad I was able to help, and if you need future help, please look me up!