My dealer swapped out the axles (gear) and transfer case (ATF) with Amsoil (that I provided) for me when I did the 30k service, no problem.

When I got my tranny done awhile back, they dropped the pan and replaced the gasket and then flushed and filled with the Amsoil ATF that I provided.

Whatever brand, syn is better than regular and most any decent mechanic will tell you that.