Ever since I had my 3.73's installed, I've had a vibration when going above 80. I figured it was the driveshaft, but had it balanced and it was fine. I tried driving it at the equivalent of 120 with the driveshaft removed, and there was no vibration. I finally took off the wheels, disks and alxes and guess what... it still vibrates above 80. So it must be the differential, right? Could something have been installed incorrectly to cause this vibration?

On a side note, when I revved it up without the axles and the diff cover off, the noise coming from there was really loud. Don't know if this helps.

 

WAG if you ran it with the cover off and no oil to look for the noise you trashed what wasn't already broke.

 

There was still residual oil on there, and it was literally for 2-2.5 seconds, just revved it up and shut off engine to see if it still vibrated. I don't think it hurt it.

I was reading on another post that vibration on deceleration (which I have a little of) can be caused by bad u-joints. Could the vibration at speed be caused by the same thing? When I took my driveshaft out, they didn't seem bad (the caps wern't loose) but I don't really know what to look for.