07 Limited heater only working on HI

07 Limited CM 4x4 w/auto climate controls. 125k miles, radiator and Tstat replaced w/Denso rad and OEM Tstat abt 400 miles ago. Coolant level is fine.
Driving home today, O/S air temp was ~60, climate controls set to "both", temp @ 72.
Noticed the heat coming out wasn't warm at all, felt like ambient os air. Turned up to 80, still not hot. Took off Auto and set temp manually, same thing.
Set to HI, plenty hot.
Engine temp was @172 (can see vitals on aftermarket stereo), just spent abt 20 mins in stop and go traffic.

Blower fan works fine in all positions, blend door seems to be blend dooring on some level, diverter works (goes from defrost to dash to floor w/o issue). AC works fine.

Just have all the heat or no heat.

Just checking to see if this is a common problem before I dive into it any further.