I have a 02 Dodge Ram 1500 that the defrost setting blows warm but the heater setting blows cold. There is also a setting for the defrost and heat on your feet that the defrost is blowing warm and the heat is blowing cold.

See if there exist Electronic Air Temperature Control (EATC) On-Board Diagnostic Tests for your truck, similar to those for Fords below:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-11.html#post1999642