Front wheels binding when in 4wd and hubs are locked?!?

[Burbinite]

A few months ago I broke the centering yoke on my front drive shaft. I have since rebuilt it with "super strength" u-joints and a new centering yoke. Now since I reinstalled the drive shaft I think I have found why it broke but don't understand what is going on.
When I shift into 4wd I hear this clunk, clunk as the driveshaft turns. I have watched it turn and it doesn't seem to be the problem. Even after driving a few feet my hubs will not unlock, even rolling front or back to relieve the load. I have to jack up the front to get them unlocked. When I jack it up whichever wheel gets weight off of it first turns backwards about 1/4 turn and with quite a bit of force, enough to chirp 33"x 12.5" tires. I have tried jacking up either right or left tires and both do the same thing. With the hubs unlocked and the x-fer case in "N" I can turn the driveshaft by hand and everything seems to work fine. I have done the same with one then the other hub locked and that seems to work as well (open front diff)
Is the problem in the diff? I didn't have the time to open it up and inspect it today. But just wondered if anyone else has had this happen. Sorry to be so lengthy but I wanted to share everything I have done to get the best answer possible. Thanks for your help in advance!!