Did you put in a new gauge, or is the same one? A new one might be more sensitive. I'd get a meat thermometer and put it in the top of the radiator through the cap hole to verify the temperature.

Radiator rebuild, does that mean a new core, or did they just check it out? Fan belt tight? Side curtains on or off? Just some ideas...

I don't like getting near the red on the gauge, so I know what you mean. I don't think a cooler thermostat will make much difference though. Once they're hot, they're hot.