There are numerous post on overheating transmission oil on the JK Wrangler. I have a 2009 Rubicon, I installed a Derale Heat Sink Cooler on the Bottom on the rail in front of the condenser coil.
The cooler is finned insided and out, and 18" long. It holds about one quart of trans fluid that also aids in cooling. I plumbed it with trans rubber hose, 3/8" diameter, in line with the fluid return line from the condenser cooler to the transmission.
Prior to the installation, I checked transmission pan temperature several times using a hand held laser. (Bought at Harbor Freight, $24) I know this is not the most accurate method for temp sensing. All I wanted was a reference temperature, before an after cooler installation.
After a 25-30 mile run on level ground, mid 60s temperature, the pan averaged 175 degrees. After installation of cooler, similar driving conditions, the temperature was 148 degrees.
I live in Arizona, so high temps is a concern.