Amsoil Severe Gear 75W-90 is my personal choice. Amsoil formulates an outstanding line of lubricants, especially gear lube.
http://www.amsoil.com/redirect.cgi?z...storefront/SVG
There are some gear lubes out there that flow like 20wt motor oil, but I've never personally tried them. Anyone have any experience with these "qualifier' type lubes?