Often forgotten on vehicles, particularly these bigger pickups, is your tranny, rear and front differentials. I religiously change the lube in them at every 15 thousand kilometers. You can get away with longer durations if not towing, but because my Ram 3500 doesn't move unless it has one of my trailers attached, I make sure it these "forgotten" parts are maintained.
2013 Ram Longhorn 3500 Crew Cab 6.7 Turbo Diesel, Aisin Transmission.
2014 Jayco Eagle Premier 351 RSTS, Mor/Ryde Suspension and Pin Box, 17.5" wheel upgrade, 18k Pull Rite hitch.