overheating 1993 Wannabago brave 27

If the previous suggestion don't work,I would use a good chemical flush first drain it, remove the thermostat and reinstall the housing, disconnect the bottom hose and clamp a garden hose inside and let it run full force. You can watch what comes out and see how fast it is draining. While the thermostat is out put it in water and bring it up to a boil, it should open just before boiling about a 1/4 in. If it still runs hot use an IR gun and shoot the temp sensor in the left head and thermostat housing and compare that to your gage reading, these gages can be off. You can then shoot the radiator with the IR gun in a 4 in grid pattern from top to bottom and look for colder spots which would indicate a blocked section of the radiator. From top to bottom you should see a change in temperature of 50 degrees. Having said all that a gage reading of 212 on a flat is not all that hot for a 454, does it recover quickly once you crest the hill or does it stay hot for a while?