Signed up to confirm this. Below are the symptoms and resolution to this exact issue.
2014 GMC Sierra Denali
Symptom: On full blast AC mode, driver's side luke warm or hot, passenger side cold.
Resolution
1. Turn ignition and power off
2. Remove negative battery cable
3. Remove fuses 35, 55, & 56 from BMX fuse panel "inspect them"
4. Wait 5 minutes...
5. Reinstall fuses 35, 55, &56
6. Reconnect negative battery cable
7. Turn ignition back on
8. Don't touch HVAC controls for 3 minutes.
9. Test Driver vs Passenger side temps
Most likely the HVAC door actuator was out of calibration and a loss and return of battery power forces a recalibration of the unit. Hopefully this helps someone needing clear and concise instructions.