Well did a 3 hr drive friday night and yester day afternoon with the trailer attached. Friday night, i kept the speed to 90km/h and the trans temp stayed around 80°C that's with a head wind. Whenni was at 100km/h the guage climbed to 110°C.
On the way home i had a tail wind, speed was between 90 and 100km/h, with a tail wind. Trans temp stayed between 65 and 80°C, depending on hills vs flat land.
As for the cooler, its a square one that takes up half of the engine rad behind the grill. (Engine temps stay normal)
The factory one wasn't cooling enough with a trailer. Was going to use both but this trip showed that in head winds i stay below 100km/h and i'm good.