So from what I can gather, Mobile 1 75W-90 Syn fluids for the diffs are acceptable as a replacement for OEM. But if you have e-locker rear diff, use the OEM one. Xfer case, use the OEM fluid...sound about right?
Yeah, 75w90 front and rear, I personally prefer Castrol over Mobil, but that will work fine. If the rear is locking, you need to either use a 75w90 with a friction modifier in it already(I believe Redline and Royal Purple both do) or a standard 75w90 and add a LSD friction modifier, but the factory fluid is just a standard gear oil with a friction modifier.
Stick with LR fluid for the t-case, it is actually a type of ATF, and not a gear oil at all.
I strongly suggest installing the updated style front differential breather cap as well, to keep it from over-pressurizing and causing leaks, cheap part, good insurance.
T-case fluid P/N LRN0753
F diff vent cap P/N LR019450