Bummer- more vibration woes

["J Staub" <jstaub@domain.elided>]

Well, this weekend I replaced the inner and outer bearings, the inner axle
shaft bearings, the front wheel u-joints AND the front axle u-joints on my
'79 Scout II. It certainly smoothed everything out- for a while. Today was
the first day I really had it out for a long run and I hit a bump and the
confounded intermittent vibration returned. This time it was back with a
vengence! I've always wanted to be a mover and a shaker but this is
obnoxious. You can feel the whole truck vibrate, but it's not an big
shaking, more like a rough hum. It wouldn't stop on its own, even after
repeated stops. I then put it into 4 hi with the wheels unlocked and it did
not return. I put it back into 2 hi and yep, it happened again right away.
The rear axle shaft U-joints are also brand new. I haven't replaced the rear
bearings, but I would swear the vibration is right beneath my feet. Can
anyone tell if I should be tearing into the front differential or the
transfer case next? Other than feeling for loose shaft play, are there any
other checks how will I tell if anything needs replaced? Finally, if anyone
has experience rebuilding differentials or transfer cases, I would
appreciate any info on the size of the job, special tools required, and
cost.

Also, if anyone is considering replacing their front bearings I could give a
few tips. The first side took me 7 hours to figure out (including 3 trips to
the auto parts store) and the second side took 1 hour. Textbook learning
curve, huh?

TIA for any help,

John Staub