gauge goes up to 3/4 way before fan runs

 

There is a lot of variance in factory gauges. A stock t-stat opens at about 195 degrees. Depending on the vehicle the gauge could read 1/3, 1/2, 3/4...at this temp..

The fan is commanded to come on by the PCM at a factory programmed temp. of 210 degree F (low), and 220 degrees F (high). Both the same for 4.6, and 3.8. The PCM knows the temp. from the ECT Engine Coolant Temp. sensor.

(Note: the only way to lower the temp. the fan comes on is by reprogramming the PCM (tune).)

I'm not sure, but I take it from the post you wrote that you mean the car is not actually overheating, but the gauge reads high.

A scan tool will tell you a more accurate reading of the coolant temp. Also, ECT values would be particularly important to read.

There is also a temp. gauge sending unit. Not to be confused with the ECT sensor.

For what it's worth I hope this information can be of some help.