2008 Rubi jk auto-Amsoil motor & Diff oil-Grade?

Getting ready to order some Amsoil. 75w-140 for the Diffs? Is a friction modifier needed?
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Also looking to change motor oil soon. What weight oil is every one using? I've always used something in the 10w30, 15w50 ranges. but thats in older vehicles. Now there's 0w-30, 10w-30, 5w30Hd. Whether its 0° or 100+° - year round? Just wondering what experience anyone has had with what oil.... Have normally used a Synthetic oil, thinking of changing to the Amsoil in the motor now too. And their oil filter too I guess. Just thought I'd get some input if there is any out there... Later all.... Also am still working on other projects, will complete those threads as I progress. Got side tracked some - Life, work....

If I remember correctly you have manually actuated lockers.....no additive necessary.