Rear end Vibrations, HELP

[iman53]

Hey guys so I have been trying to track down this vibration that I have been having ever since I swapped my diff to a 4.10
However, unless the LSD carrier can cause vibration I do not believe it is the diff. This is because I took a 2.93 diff case put in a 3.73 gearset with new bearings but using the 4.10 carrier. Could the carrier be the issue?

When I did the first pull after installing the 4.10, around 80mph it felt like something popped and the whole car started vibrating. Since then I haven't been able to figure anything out.

The vibration starts around 70 and gets worse the faster you go. It's a fast vibration like a driveshaft not like wheel balance. It feels as if it's coming from the rear. doesn't seem to change on accel or decel and it doesn't matter what gear I'm in.

Things I've tried since then:
Driveshaft has been rebuilt and balanced twice (custom one piece)
axles swapped with other used axles
wheels rebalanced
diff rebuilt
made sure everything in the rear was tight

I'm stumped!!!! if anybody has any ideas id appreciate that

[iman53]

This seems to be a common issue in the world of one-piece driveshafts. Has anybody else heard of this being a problem for cars with a one-piece and an IRS rear?

[g.ruff561]

If you don’t mind me asking where did you get your one piece driveshaft?

[iman53]

If you don’t mind me asking where did you get your one piece driveshaft?

I had it built at a driveshaft shop local to me. Called cooks brothers, they mostly do semi truck stuff I believe