No heat, hoses look to be good?

The vehicle listed above is V6 Magnum.

Coolant level is fine--just flushed and filled, once before changing the thermostat (and t-stat housing), and again after changing those two parts.

Heater hoses look to be in good shape. Upper radiator hose is hot, lower is lukewarm.

Heater core was replaced in 2013. Both hoses, to and from the heater core are hot.

Blower motor is powerful.

Once the engine has been running, air to defrost came out the warmest, though not nearly as warm as it should be. Next warmest was to the floor (again, unacceptable, as a norm). Dash vents blew flat-out cold air.

Trying to change things in order of cost/simplicity. It was overdue for flush/fill, so I did that first, hoping that anything clogging the system would get flushed. I replaced the thermostat/housing next. Still no dice. I was going to change the Blend Door Mechanism (Haynes Manual calls it the "Floor-Defrost Door Actuator), but I cannot find the part anywhere online: RockAuto, usual parts stores, Amazon, etc. I have not pulled the lower dash yet, to see if there is more than one actuator, but one online source said--given the year/make/model--there is typically only one. Again, finding that one has been a challenge.

I'm looking for other ideas, as my local shop wants about $150 to even look at it. I'm getting so frustrated that I might just pay that, but my fear is that the answer will be, "Well, it could be this or this or this. No knowing for sure, until we tear it apart and see, " which would likely end in a $1,500 bill instead.

Any ideas?