Did a testing the weekend towing the outlaws much smaller/full height 2 ton 18ft van.
Same test as before up ourimbah hill sitting on 90kph.
outside temp was about 27 again so equal test.
Good new temps were much more moderate 85-90 Deg C.
verdict was simply me pushing to hard with much larger/heavier load in the past.
cruising along was 82-85 C depant on grade so again all good.