I read this and am dying for more info... in the main rear driveshaft the transmission rear seal hold the splined output shaft solidly centered... if the seal and the case are wollered out so bad you can move it with just your hands then there is no fluid in the trans and the trans is shot... but there is no boot on any I have seen - no that I have crawled under 4th and 5th gen yet.
If we are talking front shafts on a 4x4 there are a half dozen styles and I have no idea what 4th gens have, just haven't looked at or tore one apart yet and they are too new to be in the junkyard in any volume at all (haven't seen one yet, and the 5th gen I have to maintain is 2wd).
FWIW, the only way I could see the output shaft and driveshaft knuckle taking enough abuse to do that is if it was modified (lowered/replacement driveshaft/longer trans swapped in) so much that there is no slip left in the shaft and then driven like that putting a lot of impacts (every pothole) just powered into that joint. Is this a lowered truck or something else non-stock?