I am doing 60K maintenance on my Isuzu this weekend (fluids had been changed at 40K with dino at the dealer), and I am putting 1.2 quarts of M1 Syn ATF in the transfer case. It made a huge difference in PS unit, I am sure transfer case will love it, especially in our winters.
Front and rear differentials will get ST 75-90 synthetic gear oil, plus Trans-X LSD additive in the rear.