I have been working on this and other things with Dodge ECU.
I firmly believe that it does not exist in the Dodge ECU.

The third way to measure does come up with numbers, but they are exactly the same as engine coolant temp so on the Dodge, no good.

Have you tried these…

Quote from mfifield on February 21, 2012
This might help out. I just read it on a Ram forum:

“There is already a sensor in your transmission that reads sump temperature. If you have a scan tool that will read data using PIDs, you can program it to read this thermistor. The PID was A01B on older trucks, and it is B011 on newer trucks (2007 and later, I am sure, but I don’t know how much earlier this code was used). This should return a signed 2-byte value with a scale factor of 0.015625. So you read a 2-byte value (like 11968) and multiply it by 0.015625 to get the measured sump temp in °F (in this example, 187°F).”

This link may also be helpful…

http://forums.woodalls.com/Index.cfm/fuseaction/thread/tid/25431235/print/true.cfm

Edit:

Pids 2124 and 2172 use same equation as above
but variables may be different.