As with all temperature measuring system, the indicated temperature is dependent upon the temperature sensor location. The following article, written by a fellow who builds Dodge diesel transmissions (http://dieseltrans.com/), may have an answer to your question.
http://www.dieseltrans.com/phpBB/viewtopic.php?t=558

 

that is a good read, but why would u want to monitor oil that has gone threw a cooler? wouldnt you want to see what the temp is inside the trans? Also After reading that i dont know about my mounting location of my sender now. SOme of the guys say its ok and now this guy says no, what to do ?

 

When I first installed the Procharger I had been making about 280-285rwhp na just prior I guesstimated(dyno'd 270rw before tuning w/laptop). I only had one small trans cooler so figured with boost Id need more cooling so added the MP alum deep pan & temp gauge (port is in back of pan) to see where I was at. Under driving the D-1 so it would only make 3.5psi as I got a handle on tuning it (MP PCM & SMT6) the gauge was showing about 190-195* at idle (2800 stall). Going WOT from a stop, temps would spike to 230*+. Added a 2nd cooler right away & upped the boost to 7psi. From a stop going WOT would see 215-220* spikes with about 390-400rwhp. Im sure the temps will be going higher when I finally get things back together & running boost. Probably be over 230* maybe even 240* with the 3800 stall, as I shoot for 600rwhp. (800+crank)