If you are not hearing any ticking or clicking sounds, it sounds like the air mix door linkage needs to be adjusted. Since it gets hotter, that tells me the actuator is moving.
If you look at pic 1 and 2 below, it explains how to adjust it. In pic 3, I highlighted and circled the positions of the actuator based on the temp request.
The actuator is located under the dash on the right side of the HVAC box.
Let me know if this helps or if you have other questions.
See pics below.
Images (Click to enlarge)
Thursday, April 8th, 2021 AT 8:41 PM