OEM spec is 80W90.
I run 75W90 Royal purple(RP is full syn) in both axles, with friction modifier in my rear axle to make it super slippery in the rear with my locker.
I wouldn't run anything 140 on anything on the truck.....that's superthick crap and in a colder environment, it'll goo up.
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'01 XLT disguised as a '03 Fx4 Level II.
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