Heater problem resolved!
I finally have enough heat to cook an egg!
I had decided to take the thing to a dealership to get it fixed. After reading through 37 pages of posts last night, today I decided to try ONE LAST TIME to resolve this.
Several months ago I used the Prestone radiator flush and left it in for 3 days while I drove it. I then flushed it completely for almost an hour through the radiator cap using a fitting in a flush kit. No change. After reading extensively last night, I decided it HAD to be a dirty heater core.
So I disconnected both heater hoses at the block and, using the hose, flushed extensively in both directions. I then blew (by mouth) into the inlet hose to clear most of the water from the heater core. It must not hold much since I only poured about half of the bottle of Prestone flush directly into the inlet hose while elevating it. I let it sit for an hour and then flushed it with a hose for about 15 minutes. I then repeated the whole process with the other half of the Prestone bottle and then filled the hose with antifreeze and reconnected them. Burped the system and drove it for 20 minutes. It was warmer, but didn't really kick in until I kicked in the passing gear a couple of times. Then the heat really kicked in and continued even at low speeds. While flushing the heater core, I collected the effluent and there didn't seem to be very much "junk" being flushed. But it worked!!!
I guess it helps to be persistent!