Fluid changes, can I use 75w 90 full synthetic in front differential?

Front differential- owner manual states 80w 90 gear lube - I found service bulletin PIP372D Nov. 2012 that states:

14. Myth: Synthetic fluid cannot be used in front axles on T-trucks and L-vans. The seals are not compatible and could also cause bearing failure. False -- Synthetic lube can be used in all new American Axle Manufacturing Assembly.

Can I use 75w 90 full synthetic in front diff?

Rear differential: should I remove the back plate to drain fluid and clean? No noise from front or back differentials, just trying to get another 100,000 out of this truck.

Transfer case: I have 4wd that uses a round knob to engage. It has an auto selection, what fluid do I use? I do occasionally get messages about transfer case/Stabil Trak pop up when I’m out in the woods in 4wd.

Transmission fluid and filter: is this doable but DYI? (I just finished replacing oil pump, timing chain, water pump, hoses, oil screen, camshaft sensor, crankcase sensor, oil level sensor in carport and truck runs down the road).

I utilized your rebuild 5.3 series for lots of info while replacing my timing set, thanks for great videos!