I was told yrs ago not to labour tow In 5th- ie: don’t pull in 5th- fine to coast down hill & cruising along the flats but never pull in 5th because 5th gear is tiny in most 4wd gearboxes- about the size of a 50c piece ( that’s what I was told) anyway it gets hot & cooks the oil then it destroys everything. That was in Ranger/ BT50 gearboxes & im lead to believe most others aswell so I’ve just stuck with that. Happy to be told otherwise.