97 f150 thermostat been replaced coolant flushed heater core flushed twice. Heat works but no where near as warm as it should be. If i turn my temp dial to hot or cold it works as it should but is there a chance that when i turn the dial to completely hot that the door is not shutting all the way allowing cold air to mix with the heat ie not allowing my heater to get as hot as it should??? Im gonna cut into the plenum box tomorrow and see what i find but just wondered if this could be my issue

 

You could tape off the vent above the firewall to stop outside air from coming in before you start pulling things apart.

 

An easy way to check the blend door is to check it with the actuator. Actuator is located in the lower center of dash. Behind the black trim where the floor vents are. If you remove that trim, behind there is a white box, that's the temp actuator. Remove the screws pull it out slightly and turn it. This will move the door. The door should move freely. You can also check that the actuator moves all the way cold and warm by, watching the 1/4 square drive on the actuator. It should move as you change temperature. Are both heater hoses hot? Some heater cores are set up that they can bypass the (core). Which would make the hoses hot but not inside. I can't remember how these are set up, it's been a long time since I had one out.

 

Yes both heater hoses are hot