weak heat 2008 hd 2500

as of the past month or so i have been having the same issue with my heating system. That is when i used to have my heat no higher than 73 degrees and at fan speed 3, that was perfect and i normally turned it off after a bit because it just worked very well. even right off the bat early in the morning. didn't matter how cold it was.

Now its blowing luke warm air. the fan speeds work well, and i have to crank it up to 90 degrees to get any type of warmth. its consistent too, as far as it just not working. it pretty much stays the same weather i have been driving for 10 minutes or an hour. all the vents seem to work and when i designate where i want the flow to go (head, feet, defrost) it all works. a/c works great. I re flashed the hvac system with a buddy. did the 2 therms, backflushed the heater core. topped off coolant. now i am here. first time to post to a forum. also coming from a dodge 5.9 6spd. so its a learning curve needless to say. maybe a blend door(s) issue? or hvac control module? im just stumbling around in the dark basically so any help is great before it goes to the shop

 

did you ever get this figured out?

my first guess would be the thermostats, but it already looks like you did that