Fuel pump problem?

I have a 1990 Tioga Fleetwood 28 ft class C motorhome with a Ford 460 fi 7.5L engine. After filling tank, driving for about 1.5 hrs, using about a half a tank of gas, I stopped for about 10 min and went to start back up but was unable to start it. It acted as if it wanted to start but would not. After about 20-30 min tried again to start and it fired right up and ran fine. Got down the road about 10 miles and could tell it was not running smooth, as if starving for gas. If there was any inclines in the road it was having trouble keeping speed and again seemed as if it was not getting gas properly. Drove about 50 miles this way and when slowed down the engine slowly lost power and then quit again. Waited about 30min again, put a bottle of heat in, immediately tried starting it again and it started right up. Now the fuel gauge was at about a ¼ of a tank. I replaced the fuel filter but have not run it down the road much since. Someone mentioned it could be vapor locking or a fuel pump problem. I do notice when removing the gas cap when the tank is low I hear air pressure being released. Have not had any other trouble previous to this. I was told there is a fuel pump in the gas tank along with one mid way to the engine. Wondering if this sounds like a fuel pump problem or something else causing it to starve for gas. Temp was in the 80’s when happened Someone mentioned they heard of this being a fuel pump problem when it gets warm out. If the temp gets above 80 degrees the fuel pump in the tank stops working properly. After you stop and let the engine cool down it’s fine again till it gets warm. If anybody has any ideas please respond.

try a new gas cap.