Thanks for the question.
If both heater hoses are hot going to the heater core, then more than likely the blend door actuator is bad and will need to be replaced. This is pretty common on this truck. It is located in the center of the dash just above the hump. Sometimes just wiggling the connector going to the actuator will cause it to start working. If it doesn't replace the actuator.
Next, check the heater control knob for any signs of cracking by pulling it off. Replace the knob if you see any cracks.
If both heater hoses are hot to the touch and the blend door actuator is moving, then there is only one thing left, the blend door is broken or cracked where the actuator attaches to the blend door. You can sometimes see this by removing the actuator and looking at the blend door itself with a flash light for any signs of cracks. If you find the door broken or cracked, then replace the door. This is a very common issue. I have a link below that you might want to check and see if you want to fix it this way. Looks like you don't have to remove the dash. I've never use this before so I'm not sure if it would work. Just something I've seen over the years.
If the heater core had a flow issue, you should be able to tell by a different temperature of the inlet and outlet of the heater hoses.
I'm curious, how are you able to tell the blend door is moving?
I have given you all the answers I have seen on these trucks. So I will opt out and allow another tech here for you.