My heat was the same way until Friday. Bit the bullet and put a new heater core in it. I had good flow as well. When I pulled the old one it weighed three times as much as the new one. It turns out it was most of the way clogged but i couldn't tell cause the flow through the clear tubes was hiding the issue. It's nice to have heat. If you can set aside a day and replace it as we'll as your a/c evap core since your in there.
"Of course he likes your idea. When one retard on the short bus licks the window, the others think it's a great idea and start licking like crazy!" Rob99