I have 30000 miles on my 4x4 V6 and am getting ready to change the axle differential fluid. I purchased Mobile 1 75W-140 synthetic (API-GL5). The manuel also says to use a friction modifier additive. When I went to my Jeep dealer to purchase this additive he told me that the Mobile 1 was all they used and that it already contained everything I needed and that I should not use the additive. I called the Dodge dealership and they said the same thing. I am confused because the manual says to use the friction additive. Does anyone have any ideas?