I have a 2003 Ram 3500 4WD Dually with a 5.9L. I recently installed my gauges. Yesterday, I took it for a 3 hour drive and the Transmission temp never went above 115 degrees. On the open highway it stayed between 90 and 100. In town it went to 115. Outside temps were around 20 degrees and a pretty tough wind blowing snow pretty good.

I know this is not the best spot to take the temp, but the sensor is in the Test port on the Passenger side of the tranny. That worked fine in my F250, but I did have to install an extender in the Dodge.

These temps sound low to me but I rarely used my Ford in the winter so I am not sure.

Any thoughts before I begin towing my 5th Wheel this spring and summer?

 

Sounds low to me too. I suspect that the port you are using doesn't see pressure in the higher gears..... so, you get an artificially low reading.