So does the pinion actually have side to side play and up and down-if you grab the yoke and try to move it back and forth, does it? A drive axle problem is typically noticed on acceleration or deacceleration because the gears mate on both acceleration + de accel but on opposite sides of the teeth, if that makes sense-so noises vary whether you are cruising, accel, or de accel. Does your truck make noises like in the video? The second video where he said he just 'tightened' up the rear end is mainly bull-with the exception of the nut backing off, the only way that pinion loosens is by the bearings wearing. If they are that worn that bad, the diff needs to be re-bearing'ed, that is to do it right. In a std rear end there is preload, backlash and pattern that need to be taken into account. Preload is the amount of pressure on both the pinion and carrier bearings, usually measured in rotating torque, in in. #-meaning you take all the clearance out of bearings to 0.0", then subtract clearnace causing it to be loaded. Backlash is measured typically with a dial indictor against the ring gear, keeping the pinion stationary and 'rocking' the ring gear back and forth. In the video he would have a ton of lash cause the pinion is no longer staionary, and pattern is simply checked by apply a gear marking compound(gm makes a nice bright yellow color), and check the pattern by running the gears around back and forth and checking their wear against each other. I am not familiar with this particular rear end, but if the yoke moves, that doesnt seem promising, but maybe someone with more experience with this diff could say other wise. So does the seal leak? The nice thing with these trucks is that they are a third member if I remember correctly, which would mean pulling the axles shafts, driveline, nuts around the case and yanking it out. I'll bet rebuilding it could be kinda spendy if a shop did it. Beings it looked like these were a straight bearing in the exploded view, I'm not sure exactly how they set the preload, so I guess Im not much help.