I had a car in high school that the thermostat got stuck closed and it caused a freeze plug to blow and engine to over heat because when it gets stuck closed all the pressure builds in the block.....I think you might be on the right track

 

Thanks for the info LIL. I appreciate your input.
I'll probably end up replacing it and if that doesn't fix it, then off to the shop.

 

Root cause was the thermostat. I just finished putting
the new one in, refilling and gave it a rigorous test drive.
Temperature is fine.

Thanks everybody for your assistance. I probably saved $3-400
with your help.