Cheap way....
I did this on my 5sp, which requires your to catch your old fluid or change it.
Remove the PTO plate on the side you want the sensor. I drilled the plate to accept fittings to provide a place to screw in the sensor into the plate. Reinstall plate and your good to go. I put my sensor on the drivers side so I did not have to disturb it each time I changed the fluid.
If your pulling hard and heavy, transmssion temps will move some. I find they follow the engine oil pretty close. If your engine oil temp runs steady, so does the transmission. Running empty it rarely gets to 150. When pulling hard I have on got to 190 once, but then again, the engine oil is at 220.
jjw
ND