I looked into Royal Purple Synchromax, it does not say what weight oil it is.Does anyone know? Is it truly compatible with the Getrag even if it is not 5w30? Also I was contemplating running Synthetic in my Cummins, but I burn WMO, will the synthetic be ok to burn in a light mix with mostly #2D?

 

It's actually lighter than a 5W-30, it's roughly equivalent to an ATF. Dodge suggested ATF as an alternative fluid if shift effort on a cold trans was excessive.

http://www.royalpurple.com/manual-tr...-fluid-pp.html

Synthetic WMO burns just fine.