What oil do you guys use in the Transmission, Transfer Case, and Front and rear Diffs?

Thanks

Depends, I like to mix in some synthetic if I can afford it.

What is it that factory calls for?

I run synthetic in frt/rear diff's and transfercase.If i start towing a heavy trailer the tranny will go synthetic also.

I run 75/140 redline synthetic in my nvg 4500. Factory fill is Castrol syntorque synthetic. I also preffer 75/140 in the rear axle. Transfercase depends on type, front axle, 90 wt or 75/90 synthetic.:D I preffer the 75/140 in my trans due to the power output I have and the fact that I run in 5th gear almost all of the time.):h

The old owner of the truck used 90wt synthetic, so that is what I continue to use, haven't had any problems so far.