Just started doing this. It is mostly at low speed and really noticeable when coming to a stop, almost like a caliper grabbing.
There is a point of harmonics around 40 mph and around 75mph.
U joints feel good and tight.
Center carrier feels good.
All the same temp after a run.
Cover pulled on rear end and everything looks good.
Truck was serviced at the dealer before I picked it up.
Rotating rear wheels feels smooth, nothing to indicate a bearing.
Rear rotors look good but have not been measured to check for warpage.
Weights on the drive shaft are all present and accounted for.

I was in Oklahoma a couple of weeks ago and the truck was running smoothly. I heard a clank up under the floor pan like a rock being thrown by a tire. After pulling onto the freeway, the vibration started.

Shortround is stumped

 

Maybe a tire gone bad?
on edit - I chased a vibration for quite awhile. Drove me nuts. Could not have been my u-joints because they were only a year old and I felt no play in driveshaft.
Guess what... it was my rear u joint... totally toast. Sometimes just grabbing and twisting the shaft isn't going to show you the problem.

 

Thinking the same thing. However, I replaced 2 tires and did some shuffling and it made no difference.
The lube in the rear looks like it has been recently changed. Right type or not is a guess. I'll go with a synthetic but with the limited slip having no clutches, would an additive be necessary?
Now that it's up on jack stands, I'll get some lube in the rear end tomorrow and spin it up. It "looked" like there was some wobble in the rear drive shaft. If so, that could very well lead up to a bad joint or a carrier that may need to be replaced or lowered. However, I think the "rock clunk sound" might have something to do with it.

Shortround feeling like Alice in Wonderland

 

shortround, I'm willing to bet it's your rear u-joint. Mine shimmied, shuddered, clunked, drove me freakin' nuts. Pull the shaft. It's only 4 bolts. Let me know what ya find.

 

It was the forward u-joint on the rear-rear driveshaft. Just one axis. Will swap out both of them in the morning. Kinda weird, just a week and a half ago it was smooth. Such are u-joints.

Spun up the forward-rear one and no vibration at all up to 3K in 6th.

Any recommendations on replacements? Want greaseable ones.


Shortround relieved

 

I use Neapco. Glad you found it.

 

Went with Spicer. 2 u joints installed, well under a hundred.
No vibration.

 

cool...