Ok, it's not on my '93, but you guys and gals are smart, so thought I would run this up the flagpole...
My 2002 Grand Cherokee (4.7) was making a lot of noise from what sounded like the front diff. The good diff oil I replaced a few thousand miles ago was black, so I pulled the pumpkin expecting to find carrier bearing carnage, but they are perfect. There seemed to be excessive backlash though (didn't measure yet) and the spiders are fairly stiff to move. The pinion spins fine and smoothly, almost no endplay.
Can't figure out what the issue is. Everything else (axles, hubs) are new.

What could I be missing?

 

Axle shafts? Aren't they cv style on these?

Otherwise maybe wheel/unit bearings?

Edit: also check the front driveshaft joints... Believe one end is a booted cv also.

 

Replaced axle shafts and hubs/bearings.

 

Could you paint the gears and check out backlash and pinion depth?