John Deere 85D temperature guage wrong

I have a 2012 John Deere 85D excavator. One day all of the sudden the temperature guage started showing that it was overheating. No other lights showed on monitor. I changed temperature sensor but no change it showed overheating shortly after starting. I changed the other temperature sensor right next to the first one which I believe has to do with the glow plugs if I read correctly. I also changed a temperature sensor or switch on the back side of the thermostat housing. Still shows overheating. I checked with a temp gun and the temperature is not to high it is within normal operating temperature. Things I noticed. On the monitor when first start the motor the temp guage is already partway up. I would guess 1/3 of the way up. If not immediately very shortly after starting I would say within 30 seconds. My gut feeling is the monitor has a issue but they are expensive to change with a gut feeling. Any tests to help diagnose this? Any ideas or thoughts appreciated. Tom