I have a 2011 Overland V6, ORII (no trans cooler). The usual trans temp when not towing in the city is about 75-76, on the Hwy 76-78 degrees Celsius.
My wife and I towed a 2500lb (dry) PUP trailer with about 400-500lbs of cargo across Canada last year from British Columbia to New Brunswick and back. We did the tow in July and the trans temp stayed around 77-78 degree variance (we saw 79 once in a while through mountains). Can't remember the other temps but I do remember they were very close to the usual temps.
Last week I test towed a 4300lb (dry) Jayco X213 trailer. I made sure I had a full tank of fuel, 2 propane tanks, a trailer battery and 3 passengers weighing just under 600lbs total. I test towed through the city and and about 30km on the Hwy. The Hwy tow consisted of a couple of steep hills, rolling hills, flat straight runs, mixed traffic with lots of big rigs. It was windy outside but not blowing hard and my speed varied between 90-110 km/hr. My trans temp varied between 78-80. The other temps raised some but from reading some other posts they were in the norm. I was using a WDH but did not have the friction sway control installed as the trailer is not mine yet and it has to be bolted on.
After lots of reading and looking at other trailers I'm going back today for one more test tow and if everything goes well I'll be signing the bottom line and bringing home a trailer