Actually it will help swapping the OEM syn in the diffs to a better syn fluid. I switched mine to Redline in my H2 and it's much smoother driving than b4. Weather got too bad out to do the front diff yet, but it's on my list
I would suggest looking at your manual and read the print on the dipstick to see if your tranny requires Dex III or VI (6) before putting syn in the tranny. If it requires Dex III, then go for it but I would suggest a complete tranny flush and new filter. No company makes syn ATF to meet the requirements of Dex VI (6) at this time as it's a lower viscosity fluid!!! If yours requires Dex 6, then suggest staying with GM Dex 6 OEM fluid.
Just dropping the pan and changing the filter will only get have half the fluid out and wont get it out of the torque converter unless you do the flush.
Either way, I would do the Syn in the transfer case for sure as the requirement for the TC is more than likely just Dex III ATF.
Doing the diffs is optional, but the RP fluid is much better than the OEM syn that's in there. I would go ahead and change both front & rear at about 20-25k miles to the RP if it were mine.