Finally confirmed that my heater core blend door is not working. Didn't get much done over the holidays, but dug in again today. Huge PITA. I'm actually sore LOL.
Removed the passenger seat. Re-tested the blend door motor to make sure it was working. Took the heater core cover off. Manipulated the blend door by hand to make sure it was moving freely. Re-installed the blend door motor. Can see the output shaft on the blend door motor rotating but the blend door does not move.
Heated the van up. Plenty of heat coming through the core so I don't think it's clogged. Got hot water through all lines. Time to order a new blend door assembly, drain the coolant, remove the core, install new blend door, reinstall core, and then reinstall everything else that takes so many hours to do.
If your heater stops working, I recommend just taking it to a shop if you're in your mid-40's and have a bad back
Oh well, I probably needed a coolant flush anyway.