Disaster avoided. I spent all Sunday completely flushing the system. Turns out I didn't get anywhere close to all the old crappy coolant out on the first pass and it was just stinky regardless. I most definitely caused an air pocket too I think.

Flushed, and flushed, and flushed some more and then ran water through it. Flushed the heater core again and refilled. No more air pockets and super hot air, front and back. Thank God!!