Sequence of events:

4:45pm - Left work
4:55pm - Arrived at Bi-Mart
5:05pm - Left Bi-Mart
5:15pm - Arrived at home
6:15pm - Left home
6:25pm - Arrived at park, ~ 5 miles from home, transmission hit 240 degrees coming into the parking lot...

100% in town driving!

Let the truck sit for 15 minutes or so, then drove it home, transmission sat right at 195* the whole time.

An hour later or so I drove it about a mile to diagnose, and it ran right about 175*.

This happened without warning, and everything else seems to be fine with the truck. Drives good, shifts fine, I even made a very short wide-open-throttle run (10mph-40mph) and the truck performed like normal.
I'm having a hard time coming up with much information in my searching. But I did stumble across this thread, about a transmission thermostat that can stick closed. Could this be my issue? Any other thoughts? Here's a link to that thread about the trans thermostat.

Found my transmission overheating issue.... 48RE running Hot? - Dodge Cummins Diesel Forum

Thanks for any help!

 

Well I followed the instructions of the link I provided, and cleaned my transmission coolers thermostat tonight. We will see if it made a difference tomorrow...