Suregrip additive?

You can also buy Royal Purple gear lube ! It is already in the oil ! But it is approx 25 bucks a quart !!! I do agree the Ford Racing friction modifier is really good stuff !! When I was working that’s all I kept in stock was the Ford Racing . Ford came out with a TSB years ago saying if you have a chattering problem in the rear end to use the Ford Racing Friction Modifier !!