2002 Tacoma Double Cab 4WD with 3.4L six cylinder. 217K miles. I bought it with 107K miles on it 11 years ago. First fluid changes since I've owned it, and maybe the first ever.
Rear differential
Out with unknown gray thick oil. Magnet was loaded.
In with Supertech Full Synthetic 75W90.
Transfer case
Out with unknown oil that was golden yellow/brown. It was way overfilled. When I took out the fill plug, oil came gushing out. Presumably factory fill during assembly.
In with Supertech Full Synthetic 75W90.
Front differential
Out with unknown golden brown oil. Magnet partially loaded.
In with Supertech Full Synthetic 75W90.
Results -- Pickup shifts seamlessly and quietly into and out of 4H, 4L, and 2H. Prior to this, it would sometimes clunk into and out of 4WD. Wish I wouldn't have waited so long. Since this is now a third vehicle for short-distance use (firewood, Lowes, hardware store, etc), I probably won't have to change the fluids again for 7-10 years.