I don't know enough about the Eaton 2 speed that's in the truck to determine if a higher gear set can be found. There's no tag that I can find on the axle, its an electric shift is all I know.
I was looking at this web page that seems to imply there were 2 axles (15K and 17K) and the heavier axle was only available with the 6.40/8.72 combo. My first choice would also be a gear set since the 15K axle listed on that page had the ratio range I'd effectively get to with the Mitchell unit.
If I were to completely change the rear axle I'd need to find a six lug axle since I have alot of money wrapped up in the wheels and powder coatong.
http://www.chevyc60.com/the_rear_axle_page.htm
