A Limmited Slip Differential Question

My experience with Sure-Grip is when vehicle is lifted with both back wheels in the air, if I roll the left wheel forward, the right wheel also rolls forward. It doesn't take any other force to hold them together. That may be because of light drag on the clutches but, my 2005 Ram SRT Dana 60 will spin both wheels forward on slick ice so it can't take too much pressure to lock them together. With an open differential, turn the left wheel forward and the right wheel turns backward or, when on the ground, the wheel with less traction will spin.
With my SRT Sure-Grip, there is a friction-modifier additive required when changing the gear oil.