Transmission service on Toyotas should be every 60k/6years. 50k if you are on top of it and really intend to go deep mileage.
Gear oil in the diffs and transfer case can be deceptive in appearance. They aren't subjected to engine byproducts, coolant and gas like your engine oil. Those should be 30k on schedule, but many people advise 15k if you spend quite a bit of time in 4low. I recently changed the gear oil on a 4runner I bought a couple of weeks ago. The gear oil hadn't been changed in 60k and, same thing, it appeared almost brand new with very minimal metal on the magnets, but I wouldn't advise letting it sit in there for years. also, holy hell, does gear oil stink!