I recently changed my differential oil and replaced with Mobil 1 and a Mobil Limited Slip Additive. It drove bad. It was like I was driving in 4 wheel drive on pavement. I have a 2 wheel drive. Also felt like it was holding back my speed and made noise when I turned my truck. I took it in to the dealership and they said I had the wrong oil in there and changed it to Toyota Brand. Recommend that I add BP Additive. They said they don't even sell additives for rear differentials. I found that questionable. Would I'd like to know is does the Toyota brand differential fluid already come with additive? My truck no longer makes noise now while turning, but I still feel a little drag. All of this does seem to make sense to me. Thoughts??