What gear was your transmission in when your oil and coolant temps got near the derate point? Was the transmission still in 7th or 8th gear when you got to the top of the grade, or had it downshifted to 6th or 5th? If it had downshifted, do you recall if those shifts happened towards the bottom of the grade or towards the top?Transmission temps have never exceeded 235 degrees at any time. I usually find it 20 degrees cooler than the oil when traveling on mountainous highway grades.
I'm not overly concerned with transmission temperatures, but was more wondering if the trans tuning behind the diesel was holding the overdrive gears longer, which would lug the engine when pulling a grade and cause the excessive heat buildup evidenced by the higher coolant and oil temperatures and, eventually, the derate scenarios.
My thinking is that, because of all the available torque, perhaps the Jeep engineers tuned the transmission behind the diesel not to downshift as early as it would if it were behind a gas engine. If that were the case and the driver were to manually downshift to direct or 5th gear BEFORE the coolant and oil temps started spiking, perhaps the higher RPM and reduced engine load would help mitigate the heat buildup.