Greetings Todder !
Amsoil severe gear 75W140 is the ticket, it has a cold pour point of -51 F. it also resists thermal breakdown like no other, it's the single best choice you could make to maximize performance and longevity of your drive axles.
Here is a link to Amsoil gear oils. http://www.amsoil.com/a/synthetic-gear-oil
Please contact me if you would like to buy wholesale.
Have a great day !