Somebody here questioned why I recommended the Motorcraft (ford) additive, when Mopar also offered a friction modifier.
I answered that I haven't tried the Mopar stuff, I HAVE used the Motorcraft, as have all my friends, one of whom owned a rearend shop. We KNOW it works, that's why.
The fact that I think it's cheaper than the Mopar stuff helps too.
When I bought my Dana 60 rear ends from Dr Diff (he gets them from Strange) both of them came with the Ford additive. Stinks to high heaven but no issues. Also used the recommended 85w/140 Castrol diff lube.