I had a similar "transmission overheating" issue with my Rubicon last summer on Taylor Pass. Contacted a local Jeep dealership and spoke with their service dept. They recommended running in 4 Low because the gearing takes a lot of the work load off the transmission and lets the transfer case do it more efficiently. Had no further problems after that, altho I have since installed a tranny cooler anyway because I'll be pulling an AT Chaser this summer.
2008 Rubicon Unlimited