Your better off just buying a set of new hardened axles.. why just upgrade to 31 splines, when you can get 31 spline hardened axles for not much more... I would tell you to buy them from www.tomsdifferentials.com , but they are on back order, for at least another month (dammit, I need a replacement for one I bent)... They sell for $220 for the set... What you can do to save money is to buy a 31spline trac-lok from an f-150, or maybe explorers....