When you changed to the Edelbrock pump you made the bypass system functional and now require the thermostat to meet that need.
My car had a Weiand pump which does not have the bypass provision and it used a stat like your "PI" stat.
Its worth investigating to know for sure.
I would question Georges advice also, ever since the hot chick avatars and alcohol product placement in his pictures dissappeared I have been worried about him....
