Rumble strip, washboard like vibration with deceleration

Hey guys looking for some help!
I’ve been scouring the threads to find some “ah-ha” moment regarding my issue. My 2013 had been having some slight vibrations at slow speed decelerations…which became progressively worse then the loud rattle started.
I have a 2.5 OME lift with the Dakar medium duty leafs, it was installed with the carrier bearing drop. Upon reading the threads I was sure it was a u-joint or carrier bearing issue due to the lift. I took the drive shaft to a shop had new ujoints and carrier bearing installed. Didn’t help at all. Then I added a 2 degree shim to the rear leafs, didn’t help.

It definitely only happens off the gas and coasting or breaking at slow speeds. My tires look good. I’m not getting any extrme vibes at higher speeds…only slow speeds about 15mph to stop. I took a selfi stick and got a video if anyone has experienced this I’d really appreciate the insight!https://youtu.be/VBJfwGaZhB4