RE: Limited Slip Differential Fluid?
I didn't read the entire thread, but there is a lot of apples to oranges compaisons here. The 2500 uses no friction modifier in the newer trucks as they use a totally different type of unit that does not use friction clutches. Friction modifier is supposed to be used on friction type units even if you use synthetic lube. The 4 oz vs the 5 oz spec on how much modifier has to do with which year and rear end manufacturer was used. The older Dodges used the Dana differentials and they called out a 5 oz. spec. I know because I had a '98 with the Dana. The newer trucks with the American Axle rear end uses 4 oz of friction modifier. Dealerships in my area get around $8 per 4 oz. bottle. The older trucks also did not spec out synthetic rear lube as they do now and the viscosity spec changed with that as well.