Now that's pretty sad that a company that big can't supply an answer to a simple question about their own product. I have used Valvoline since the late 70s in all my vehicles with no problems and see no point in changing what's not broken.
However, I have switched to using Royal Purple in my transmission with good results, having the 6 speed and when I bought this truck it had a slight grind going into 3rd gear every so often, I have not had that grind since the switch 2 months ago. Shifting is much smoother as well. Time will tell. When I bought this truck at 47k it had factory fill for all gear oils. Now at 52k all has been changed and everything runs smooth.
Good luck in getting your answer, I don't know it since I've never used Mobil oil.
Hi Jandy - Mobil 1 Synthetic Gear Lube LS 75W-90 contains special friction modifiers designed for limited slip-type differentials. In most applications, the addition of special LS (limited slip) additives is not required. For axles requiring the highest level of limited-slip performance, OEM specific LS additives can be added to this fluid. Thanks for using Mobil 1!
They could theoretically claim they put it in ...but that statement covers just about every situation on the planet. I've always used Mobile 1 and the changes they've claimed over the years never cease to confuse the crap out of me (to the point they're not believable).
We have used Amsoil Severe Gear in our Corvette diff. That's a highly recommended oil for the corvette diffs and its worked great. Not easy or convenient to get a hold of.....
Doesn't matter..... diffs are done, chatter is gone (after 1.5bottles). In 3 years from now when I'm ready to do it again - things will probably be different and confusing once again.