Buick Rendezvous all vent heat warm not hot


04 Buick Rendezvous auto 124K AWD 3.4 litre all vents blow out warm air not hot.

I tried to locate the heater core hoses at the firewall by looking behind the engine from above and below - its rather tight and hard to see - I could not locate the heater hoses by feel either - with the engine running at operating temp I would like to touch both hoses to see if they are hot - I am leaning toward the thermostat being bad - thoughts? or maybe heater core?

FYI - I have also observed, especially during the winter that when turning the driver and passenger HVAC knobs clockwise the digital display of temperature increases very slow or doesn't increase or actually goes down or will climb up in 1 point increments to a point (68 to 70 degrees) - once the car's interior is somewhat warm - I can then bring the digital display up to 90 - also the adjusting of the knobs with the interior warm then operate properly temp readout progresses up or down as expected - is my HVAC control system going? - temperamental when its "cold"?

Blend doors work without issue from Defrost to Panel to Floor - all blow only warm air.

FYI at "90" vent air is still just warm.