Had my truck at the dealer for a new def level sensor a few weeks ago (no surprise), they said I should change my trans fluid bc they could tell the filter was original from new. Truck has 73k on it. They also said I should do the diff/transfer case for the 4x4 system. All totaling over $1000 so I held off at the time. My buddy has a 2015 LML with 150k+ miles on it and he says he’s never changed the trans/diff fluids and has had no problems. What are your guys thoughts on this? We both do medium duty towing of trailers from 5-10k pounds but only between may-September once/three times a month