I run
Amsoil 75W90 Gear
Oil in my Richmond Transmission and my locker diff.
It shifts much better and lasts longer than petroleum lubes. Not to mention excellent cold weather performance should you enjoy that kind of fun in your open cockpit hot-rod.
Here's the
Amsoil info on the Gear
Oil, you may not need the slip stuff if you have a locker rear. It's primarily for limited-slip diffs.
https://www.amsoil.com/storefront/fgr.aspx
https://www.amsoil.com/storefront/ada.aspx