I am having something similar. I had a small leak around the thermostat housing so I replaced the thermostat and gasket and upper radiator hose (it was swelled in areas) i had heater for over an hour or so when I first got it done. parked it it has been 2 weeks, I let it warm up and all I get is some lukewarm heat. It has been flushed out I have no clue whats going on now.

Side note (gen 1 Blower Motor cleanup):

If your blower motor is going out or has totally stopped like mine did, you can pull it out of the vehicle and tear it down to clean it.
I had been dealing with a dying blower motor all this winter and it finally got some attention with some PB blaster fluid and compressed air (and a bit of the old brass wire brush). The blower motor looked as if satan himself took a dump in it.
Disassembles just like a little starter motor.
The hardest part was removal and reinstall...and maybe searching for one of the tiny brush springs on the garage floor.

-jeff

PS: I removed the negative battery terminal before I did this for fear of frying the ECU. It's under the blower housing and had to be pulled out first.

I was reading the service manual and trying to better undestand the water valve and the damper lever on the heater core. How is the best way to check this? I have felt my hoses and the return hose is warm but not as hot as the supply line. I have luke warm air. So I know I am getting some flow which is good, but trying to see if it is my valve is not opening all the way open or a partial clog. any helps and pics of this check would be great. The diagrams are decent but actual pictures help out so much more. Thanks yall.