You'rs is similar the heater in my 38. If your fan, thermostat & core are working OK it'll put out enough heat to run you out of the cab. If your truck isn't coming up to temp you have a thermostat problem. It's either stuck open or opening at too low of a temperature. Once you get a good thermostat in the truck, if the heater still doesn't put out enough heat, check the heater hoses. If the hoses don't get hot to the touch with the engine at full temp, the core is plugged, not allowing the hot coolent to circulate through the core.
