We did this Saturday on a 91. 5 4x2. Let me tell you how it went.
We have all the right tools. Expensive OTC ball joint tool with all the adapters, killer compressor, good tools like Snap On, IR, etc. We even bought the $61 Snap-On 2 1/8" 4 point balljoint socket.
The job took us 8 hours to do one side. I'll admit, there was a litle goofing off (maybe a lot), and a lot of grease cleanup to do, but regardless it was a hell of a job.
The previous owner knew the joints had problems and just kept greasing and greasing, there was grease packed in every orifice of the truck, including the rotor, caliper, all in the brake pads, everywhere. Took quite a while to just get all that cleaned up.
Getting the upper unscrewed was no big deal with a good impact and the right socket. Getting the ball joints unseated from the knuckle though, especially the upper, was a real pain.
When we got the lower out, it fell apart into 5 pieces. The ball itself was broken in 3 places.
Part of what took us so long was running back to the store. The door jamb says he has the 3830 axle, but when we matched the parts the ball joints didn't match. I don't know if in 91. 5 they went to the 4000 ball joints, but when we took back the ones we had and matched them to the 4000's, they were a perfect fit.
I should have taken pictures of all this. Let me tell you what you are going to need:
A good impact wrench. It might be possible without, but you are going to want it.
The 4 point 2 1/8" ball joint socket
A good, long, heavy prybar
A good set of balljoint tools, the C Clamp looking style, not a pickle fork.
Everything else is just normal tools. We found it much easier to go ahead and remove the rotor, and this is a good time to put new grease in the bearings.
AutoZone has the parts a lot cheaper than anyone else we found, and the difference was huge. We used PerfectCircle, which I've had good luck with in the past, besides it's probably what was there from the factory considering they are Dana/Spicer parts.
I realize your 4x4 may be different, this I don't know, but get ready it's a job.