My old 1991 was the one of the rare cases. I bought it and the PO had just changed the fluid in everything; the tranny started shifting strangely about a month after I got it, and when I took it to a tranny shop, they told me it needed a rebuild. I went by a Jeep dealership on my way home and popped in for a second opinion. I got a mechanic who was willing to take a test drive with me, and he told me this:
The PO must have never changed the fluid for years, if ever. When this happened, gunk will slowly start to build up, and when he finally changed the fluid, the new detergents and cleaning agents in the fresh fluid started loosening the deposits. Those deposits came loose, and stated gumminng up various parts. The mechanic said 'usually the 4.0's and these automatics are bulletproof, but once in a while this sort of thing can happen.' His recommendation? Drain a pint or two, and replace it with Lucas tranny treatment.
It worked very well, and that transmission is still serving happily in someone else's XJ.
I think in your case, that the service interval isn't too far off. I'd go for it and if you get a problem, try a tranny treatment like Lucas.
HTH!