Re: Front and rear diff fluid change
If I say anything other than the OEM recs I'd be doing so without evidence:...............but.......... I change mine early the first go around as the gears need to wear in some in anything mech. I think 4 years or 30K miles is reasonable, but the recs are more like 60K on the diff I think, and 100K or never on the AT..
I had my ATF changed during a TSB for my tranny so it was free at 22K, now I won't change that until it is due as it has been nicely warn in. I find much metal in many fluids I change in many different cars I've owned. I'm not saying that I know it harms the gears to be there, but it can't help the fluid stay in spec, and it can't hurt to change it if you have time and a few bucks and wrenches. The ATF is harder to change I suppose, so wait on that one.
If I was paying someone to do it, I'd go by Jeep's recs. But the fluid is cheap and easy to change yourself (except maybe ATF, which I haven't done yet)..
If you tow, do it 2x more often, I suppose.