Ranga, after some period of trial and checking egt's I found that if you lug up a hill the temps go up rapidly and simply changing down reduces temps very quickly. Highest I've seen are 425c and this is with an auto in OD 4th, when the OD and torque converter lockup are over ridden the temps quickly/immediately reduce to 250c at 100kph
Probably due to increased revs/ airflow/turbo boost, so changing down is worthwhile especially when towing. Normally I tow in 3rd (4 speed auto) and especially before a big hill. Just adds more to the idea that towing in top gear is not good for your donk. I suspect driving uphill in a manual in 5th gear would produce similar results, hence change down a gear or two if you want to keep it cool. Just my 2 cents
And for those with autos and fitted torque converter locking, take care when towing! Especially uphill.