5.2 magnum, auto, extended cab. Vacuum hose that comes out from firewall is connected, I did flush the hoses/core in both directions (engine off) and it did flow clear, but not great volume (control valve closed?). Also, moving knob from cold to hot when running makes a difference in the sound of the airflow (Door moves).

Is this one where the whole dash has to come off to access the valve? Suggestions?

There's no coolant flow heater control valve inside the cab.

If the coolant flow through the heater core seems restricted, it's because the heater core is plugged up internally.

Back flushing it helps sometimes to clear it out.

Thanks for the reply. Yes, I ran the hose both ways and the flow was okay, but not great. No junk got blown out.
Between this and the info in the 98 Ram heater thread, I guess I've got my work cut out...
Frigid temps and snowing right now means it's not getting fixed in the near future.

Confirm the water is up to temperature before chasing heater problems.