Update - FIxed
The problem turned out to be the actuator(?) in back of the radio just as described in the Naxja thread. Plastic rod 'pops' out when you select the windshield de-frost button. I was able to push it back in, although it keeps popping out at high fan speed (3 or 4). Once I manually pushed the vent in position, though, the air comes out of the top windshiled de-frost position.
I have a hunch I'll have to fix it again though in time.
(thanks for pointing me to that naxja link, saved me a bunch of time!)
1999 XJ 116,00 Desert Sand.
RIP: 1995 Jeep Cherokee Scrapped at 176,000