Bent Axle? (Video Inside)
I would throw down on some quality aftermarket axles (Moser, Strange, etc.) with Timken bearings and not look back. If you're concerned about the build quality of differential, check it out while you've got the back off and the oil out.
I can say, in my truck, the cold weather combined with having poly body bushings, causes my truck to vibrate. In the spring, it goes away. There is definitely something going on with that drum you showed though.






