I'll post my experiences here, so others can know / benefit if this happens to them. I've got a Jeep Grand Cherokee 2007 with the V6 3.7L engine. It's a 4WD with the 'Mercedes' transmission.
Once this week, I started out in the morning, when it had been ~35F overnite. Transmission in limp-mode. there was a status on the dash, "TRANSMISSION OVER TEMP" where the temperature is usually displayed. Check Engine light on, as well as the "ESP BAS" light. Would not advance from 1st gear. Pulled over and stopped/restarted engine. Everything OK after that. --until the next morning.
Same thing, cold morning, and transmission in Limp-Mode. This time I couldn't get it out of Limp-Mode, no amount of stop/restart would help. I had to stay home from work, so I decided to try to avoid a repair... I took terminals off the battery for 30min, then re-connected - no dice. I then decided to rip apart the center console and take the shift-module out & clean it with isopropol alcohol. Re-assembled, and no change. Still limp-mode.
After working for 4h on it, I called the tow truck & towed to the nearby Jeep dealership. I've got a service contract on this jeep, so I'm not too-too-woried about cost. Awaiting call-back. I'll post status here, just so everyone can benefit.