GL-5 for diffs, GL-4 for transfer. Unless there has been contamination, these can easily be 100k fills. I initial-filled with 75w90 synthetics early on (10k break-in?), now at 210k and a recent (2nd) change, everything was still gorgeous, very little magnet residue after 120k OCI. How many miles on yours? How does the old fluid look? Running the 4wd occasionally is a good thing for lubrication. My Gen3 hybrid LSD does not require anything beyond gear oil, but yours may be different.