There is an interesting thread in the 2015+ MQ/MR models regarding temperature issues with certain bullbars not having enough ventilation.
I got a Smartbar some time back. After installation I found they removed the Air Dams that assist in pushing air back into the radiator etc. That was a bit of a shock!
I my mind there is no doubt under towing or going up hills the temperature rises (ecu scanner) higher than it normally would, therefore the bullbar has had an effect. It cools down quickly once the pedal is off, and is OK on flat areas.
If I towed a van all the time, I would be considering a 3 core radiator to help.
In hindsight, doing only a few bush trips a year, I would not have installed bullbar. Look at the genuine Mitsy bars, which allow plenty of air into the front.