Differential fluid thoughts/recommendations...

I run AMSOIL 75W-90 in both axles. Another advantage of the finned aluminum diff cover vs the oem stamped steel is better heat dissipation. The dip stick tube is a nice feature too. The oem's invest billions of dollars into the engineering of these trucks but at the end of the day it's all about profits. The stock stamped cover will get the axle beyond its warranty and that makes the bean counters happy.