According to Amsoil, limited slip additive is not necessary when using their oil. I have personal experience with Mobil One syn. 7590 with which they make the same claims, and that their oil would not work properly without the additive. Our situation is severe service since we have a large slide in camper, which we have had weighed and the total weight for truck and camper was 10,800 pounds. I would like to know from the members who have put the Amsoil series 2000 7590 in their trucks under severe service as to what their opinion, on the need of the limited slip additive.