A loose yoke usually indicates there's bearing wear behind it. Unless the nut has come loose, there's no reason for the yoke to suddenly develop any looseness because it's tightened to hundreds of ft/lbs of torque, and usually cotter-pinned into place. If the yoke is wobbling, the preload is completely gone. so it's wise to do a complete teardown and inspection.
If the center section of the axle can be unbolted at the front, you've most likely got a HO72 axle. If there's a one-piece housing with only a rear cover plate, it's probably a Dana type 70. (Mostly used in GMC's)
Jerry
