AFAIK, for the LSD, Ford calls for 75w120 + friction mod. I haven't seen 75w120 anywhere but at the dealership (figures) and it's like $30/Qt.

Redline makes an 80w120 syn lube with goes for about $8/QT. I'm probably going to go for that - Redline is a great company.

I think the usual axle for these trucks is the 8.8, unless I'm mistaken.

XXL