I changed mine at 20k and sent in a sample. It came back pretty bad, so I drank Ron's Kool-Aid and ordered the Amsoil fluids for both diff's, transmission and transfer case. I'm at 47k now and changed it again a couple months ago but didn't send in a sample. It looked better than the Mopar. Just ordered another batch of Amsoil and another filter package from Geno's.
Good man!!! I have been drinking the AMZ/OIL elixir since 1973 and feel great!
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