I'd like to change front and rear diff fluid on my 2006 FX4 Level 1.

I know for the rear I need the XL-3 friction modifier from Ford so I will be getting that. My question is about Ford making changes to the oil type.

The owners manual says 80W-90 weight front and rear, but I keep reading that Ford released a TSB stating that all weights should be 75W-90 from now on.

If that's the case:

1) is it 75W-90 front and rear, or just 75W-90 rear and 80W-90 for the front?
2) Where is this TSB if there is on?
3) is synthetic OK to use for front and rear diffs? I have a suction pump and will be siphoning out fluid vs. changing the gaskets.