Poor cab heat
 

My duramax has 194000 miles and my truck engine warms up but I have very little heat but it's warm air so blower motor? Seems to have the fan running help?

try using the recirculation of the inside cabin air rather than the outside air. you may have to select the setting for the vent and floor board.

when was the last time you/anybody changed the cabin air filter?

Sorry to ask where is the cab filter

inside on the pass side floor. 3 screws, removed kick panel. then 1 screw to remove filter door.