I have a 2002 Dodge ram 1500 quad cab. v8
Heater does not produce enough hot air, usually around 90 deg.
Within the last couple of years, it has had a new radiator, new heater core and new blend door.
I checked all the heater doors by creating a few small holes in the plenum when I replaced the blend door and they all appear to work fine.
I back washed the heater core and it worked really good for a couple days. Then back to little heat. I took to my mechanic and with the same results. Actually, I took it back to him later and he did the same thing again with the same results. Last summer I flushed the whole engine and used a cleaner on it. It did the same thing except the heater seems to be working slightly better.
I thought about replacing the heater core again but that doesn’t make any since unless it is partially plugged and isn’t being completely flushed out.