B52Gunner,
It could be the Ranco heater control valve, but I would check the heater core for any blockage before rebuilding or replacing the heater control valve. Disconnect your heater hoses and flush the heater core with a strong spray of water from a garden hose. That may correct your heat problem. If you have to rebuild the Ranco valve Jim Carter Truck Parts offers this service with your own core. Not sure of the cost. If you choose to rebuild it yourself, it is not too difficult.
