I guess I need a pager
Mopar has a friction modifier that is added separately to the Mopar differential fluid. If it is not already in the gear oil they gave you, you will know quickly as the clutch or cones inside the SureGrip/Positraction (whatever it's called now) will not slip properly and begin to chatter around slow, sharp turns (like parking.) Even though you want both wheels pushing the vehicle, there still is a controlled amount of slip in the differential so that turns (inside and outside tires traveling at different speeds) can be done smoothly.
Recommended transmission fluid was Dexron IIE, then III, then the light gear fluid in 75W-85. Guys! I'll take this example to show it's the additives that matter, not the base oil or type!! Yes, it's a little quieter with the gear oil in it, but all the friction, wear, oxidation control, cleanliness, etc are delivered by the additives rather than the base oil. Yup, mineral ATF works as well as synthetic gear oil (excluding NGR) in this case. OK, off my soap box... And there was no supplemental additive for transmissions.
Steve's fluid change concern should be personal preference for shift quality, as the last vehicle sensistive to seal swell or shrinkage with synthetic base oils was a Mazda rotary (which burned so much anyway nobody could tell.) The European OEMs have so many seal compatibility requirements (for materials not even used anymore) that there should not be any issue with any post-80's seals or gaskets.
