2014 Ram 2500 3500 towing change axle oil every 20,000. I don't do the front that often because I don't tow in four wheel drive. The first diff change is the most important and should be done regardless of towing frequency. It removes any initial breakin particles. Axle lube changes after the first one will probably look lighter in color compared to the first.
Brake fluid is hygroscopic, I'll change mine at 5 yr/ 80,000. I also push the pistons in one at a time and then out each year.
Anti lock brake systems can be difficult to bleed so don't introduce air.
Power steering fluid at 97,500