OK enough of the BS, wild guesses, let's try this next stuff.
Before you waist any more time and money, pull the sensor on the rear head. Take it to the kitchen stove when the ol'lady ain't around and drop the sensor end in a pot of water. Don't let the sensor touch the pan surfaces, just the water. Hook up you ohm meter probes to the sensor (you may need aligator clips on the ends of your probes) and read the resistance of the sensor and record them as you slowly raise the water temperature. At the same time use your IR thermometer (or a cooking thermometer for those of you who do not have an IRT (InFrared Thermometer) handy to read the water temperature or the sensor surface temperature.
Then go to the published data of temperature versus resitance for that sensor to see if it is working right or not!!!!
Opps, now I have done it, where is that data? If I had to guess I would say it is the same as the IAT (MAT) and the CTS, since they love to use the same parts to cut costs. Does anyone have any different data for the Gauge Temperature sensor in the head?
Here is the CTS, IAT or MAT values, again!
212 F - 185 ohms
160 F - 450 ohms
100 F - 1600 ohms
Anyway, my point is I have found that my dash gauge almost exactly matches my IR readings at the thermostat housing and the rear head where the gauge sensor is installed, there is almost no difference between the actual coolant temp and the head and thermostat temp of a warmed up engine.
He should trust his IR gauge and not the sender gauge as I have read others hear having problems even with new senders not working right for various reasons including being bad right out of the box, or having trapped air right under the sensor, etc.
I am not buying the water pump idea based on all his other data!