Hm.
Well, I just tried it with DashCommander. I didn't see anything related to transmission temperature.
I then downloaded Torque and setup the Jeep/Chrysler/Dodge PIDs, which caused Transmission Temp to show up on the list, but it still didn't read it.
After looking into it closer, it looks like Transmission Temperature is not a standard PID and is manufacturer (and possibly even model) specific, so you'd have to find the PID for the transmission data point your looking for.
I don't see why the Kiwi PLX wouldn't read the PID, if you knew it. However, you'd also have to know the math correction value to make the raw input make sense.
Seems like it'd just be easier to add a transmission temperature gauge, sadly. Would have loved to get this working.