I have a 94 5.7 that is overheating when accelerating moderately hard, or under a load etc. Heats almost instantly. It cools down back to normal almost as soon as I pull over and open the hood. Gauge goes up very quickly. I replaced the thermostat with no luck. After I parked the truck and it sat for 48 hours, the upper rad hose was still hard and there was some pressure when removing the rad cap. The expansion tank and inside the rad look clean, and the oil on the dipstick looks normal. Can a rad cap cause this type of issue? I’m leaning towards a head gasket issue, but figured by 48 hours the pressure would release from the cooling system back to the blown head gasket issue?