sprint
a certain ammount of heat will be produced to do a certain ammount of work (i think its the second law of thermodynamics)
so going up a hill pulling a van you will get increased heat in the engine or increased heat in the transmission .
if you keep it in a lower gear, you are making more of that heat appear in the engine and engines can generally tolerate that better then transmission.
when you heat up tranny oil, firstly cvt oil is very expensive and secondly its a lot harder to change (the issue of sealed units

).
engine oil is easy to replace.
dont listen to this mumbo jumbo about 15 or 20,000 km service intervals.
do your oil twice as often as they recoomend and use a good quality synthetic oil.
especially if you have a turbo.
dirty oil wont lube your turbo as well, it will create more gunk to clog the intake it will clog the DPF, it will affect the CAT and when the CAT gets a bit clogged , the engine heats up as exhaust gases cant escape as well.
there is nothing better you can do then change it all the time as well as your air filter and fuel filter . and your radiator fluid , brake fluid.
dirty fluids act like cutting compounds and they wreck seals .
change them all the time
even get a big 50 ml syringe and change a bit of your power steering and brake fluid every 6 months so its always getting a freshen up