From reading I know this topic has been touched on what seems like a few times. My particular case and vehicle is as such:
I have an 06 Grand Cherokee, 5.7 Hemi, 545RFE Transmission. The what appears to be notorious Trans over temp message likes to show itself on my message center.
Going into what I've checked/ noticed..
The fluid level/quality is excellent. I don't actually belive the transmission to be overheating. I think this because I can turn my vehicle on after it's been sitting over night and the message will appear almost no time after the engine has started. While using a Snap-On scanner I noticed while the trans temp reads about 117 degrees the voltage for the trans temp snsr is about 1.75 volts if I remember correctly, however I havent been able to find any literature to indicate the temp/voltage/resistance relationship with the thermister. When the message appears the fan kick into HIGH HIGH mode for a few minutes and then returns to its normal operating condition. There is no issue felt with driving as far as shift quality or timing is concerned. I pulled codes for the trans and the only thing stored is a P0128: High Temperature Operation Activated, in a history status. Yes, I understand that should be related to engine cooling but I pulled this from the TCM. I double checked the PCM and this and no other codes were stored.
SO to summarize: Trans over temp message, not actually over temp, fluid good, no erratic performance, fans operate correctly, message intermittant. oh and no check engine light associated with the concern.
One more thing I notice.... the appearance of the trans message also seems to coincide with a Service 4WD system message, but I think I narrowed that down the the 4 Low switch being defective. Codes associated with that (active codesd) C140F, C1402. Transfer case switch voltage erratic and voltage high, respectively. Thanks and hopefully you didnt fall asleep.