Found my dads original 1971 duster!

Just my 2 cents here, but I think you need some consistency in your temp measurements, you are measuring at different places, and reading from a laser thermometer and a dash gauge, either which may or may not be accurate. If this was me, I would put a new temp sending unit into the factory location and wire that to a good Autometer temp gauge and go from there, that way you have a consistent reading every single time you look at the gauge. I cant imagine trying to diagnose a problem without having consistent data.