I realize I have not responded to the posts here, my apologies. I'm still not sure what is or was going on, but it seems to have stopped.. for now. Maybe because the ambient air temps are cooler? Or because after blowing three gallons of antifreeze ( 6 gallons mixed) I am running only water for now.

Pressure test: It was on the overflow bottle, though I did not check the change of the water level. Here is a possible clue though, at least for the boiling: Even though the cap tested good, I decided while hot to take the pressure cap off of the reservoir, and I had no pressure! Just for shits and giggles, I stuck an o ring in the neck of the bottle and tried again, a 30 minute drive I still had coolant, but no pressure! Oil is still clear, plugs look normal, not like when you get water in while running. And for the last 200 miles, I've not lost a drop of coolant.

It's a weird one!