This issue started out happening only occasionally on longer trips in hotter weather around 200 miles. A mysterious warning would come up on the center display saying "SLOW DOWN!" with a thermometer. I did not know what it was, but I knew it wasn't the engine since the engine temp was normal. It would go away after letting the car rest for 5 or 10 minutes. No regular service or transmission shop has been able to figure out the solution. A few different dealers have said they can't figure it out either. The issue has become much worse now that the vehicle is over 120K miles. I can only go 30 or 40 miles on the highway before the light comes on and I have to let the car rest. No solution yet.