Here are the facts:
1. The temp gauge intermittently reads hot, sometimes to the red
2. The indicated temp can read hot while driving at speed, or while slow/stopped, but usually is a slow/stopped thing
3. The temp gauge has been calibrated, and is believed to be correct
4. When the temp is reading high on the gauge, the temp on the sensor frame does read high, using the laser thermometer
5. No change, with the shield installed or not
6. No change, with the thermostat installed or not, although different thermostats have been tested
7. The CTS reads 188 or 189 (laser thermometer and ECU), even when the gauge reads hot
8. The coolant fan does come on on occasion
9. The temp gauge sometimes jumps around, sometimes as much as 3 tic marks
10. The coolant system has been flushed and burped 3 times, with no change
Other relevant facts:
1. No temp issues, prior to swap
2. The radiator and coolant hoses have been replaced, still no change
3. The car can sometimes be driven for hours, with the temp staying normal
Any ideas?