auto hubs are very easy to take apart and put back on. there should be 6 screws around the face, undo those and hub pulls off. if I remember right there are spring clips on the hubs hold the insides of the hub, remove those and inspect the insides. if nothing is broken inside you should get by with cleaning everything inside including the hub and put back together. the springs inside are the usual problem as to loosing tension. once everything is lubed up ( I use wheel bearing grease for boat trailers, won't break down, if going in water, as fast) put back on the truck and test.
also look at this thread
http://www.nissanforums.com/showthread.php?t=111865
