If I had to put money on this I would be looking at a front diff issue.
even cheep parts should last if all they are doing is spinning
bearings going out on the front diff
even if it is the pinion bearing going bad it could cause the CV's to go bad
good example of this kind of stuff
at work we have a LARGE truck ,55,000#+ worth of truck, rear pinion bearing went bad and the truck would vibrate noticeably at highway speed ,65+ under that it was fine
Now this truck has 12 tires on it and they range in price from $600 to $250 each and the tire company said this is probably the cause but you can not balance truck tires so just let it go until the tires need replacing ,so they let it go
well 20K miles later it got a good oil leak between the engine and the transmission ,rear main bearing went bad
long story short a $500 repair to replace the pinion bearing ended up costing close to $20K ,engine and trans over haul
and then it was discovered that that bearing was bad
I would not have replaced the front drive shaft with another oe style shaft I would have converted to use a TJ/XJ style front shaft and I would have done the same in the rear add an sye to the T-case and bam done and U-joints for those shafts are $15 each and can be replaced 100's of times
you may want to disconnect the front shaft and check for play at the pinion
also check to see if there is up and down front to back movement where the CV shafts go into the front diff
if you find play at these points then this could be it
and look at it as a blessing ,you get to not only do the above mentioned up grades but also get to put in a True Track
heck yeah
