I got home yesterday afternoon and flushed my heater core... this time doing both hoses
I used the method of disconnecting the heater core hoses at the heater control valve and flushing it with the water hose. After flushing, I took the radiator cap off, ran the motor till it got nice and hot, and burped the system by squeezing the upper radiator hose and the heater core hoses. Basically all the hoses I could trying to get any air out. Quite a bit of air came out. Every time I squeezed and air came out, I was able to add a little bit more water.
I had to take a couple hour break so that I could go to my kids school function, but when I came back I jumped back in the truck, started it, and took it for a ride to the local gas station. To my amazement when I turned on the heater, out came HOT air. WHOOT!!! My guess is that it was air in the system and burping it and flushing the heater core got it out.
The true test will be tomorrow morning on my ride to work at 5AM after the truck has sat for over 8 hours.