Honestly, yes. Unless you've cooked your fluids there should be no reason to change them out until 100-130,000kms. I'd swap tranny fluid at 60k and do new plugs, but not much else would really need to be done. Gear oil is extreme duty oil by nature, so it can go a long time before needing to be replaced. Now, there's nothing that says you don't have to swap the fluid for better stuff like a quality synthetic, but it's not a must. If it's a new-to-you truck, then it might not be a bad idea, just so you can open up the cases and see what kind of wear you have going on in them.