You said you changed tires and rims. but that could be the problem . Balancing the tires don't fix "out of roundness" , You just might have put on something that had the same problem but not have been noticeable on another vehicle. If the diff is vibrating , most likely its the tires or the shaft. Do a few things first that don't cost too much time and money .
Put a hose clamp on the shaft near the pinion , mark where the screw is , rotate about an inch at a time until you find the sweet spot. If you find a position where the vibe is less but still isn't gone , add another clamp. If this fixes the problem, have the shaft replaced with a known balanced one or have your original balanced.
If this don't fix the problem, go back to tires and have them checked for eccentricity or out of roundness at some qualified shop, not at Wally World or some other fast part outlet . Let us know how it works out .