Shudder like No Other!!!!!

Hi all... Ok, I have a little problem I cant figure out, and it drives me nuts! When cruising at normal speeds I sometimes get a shudder from my rear end and it can last for almost 20-30sec. sometimes. I dont have a lift or anything, its all stock.
Its almost like when your towing an empty trailer and it hits a bump and your truck start to shudder bc of the bouncing trailer. Thats what its like.....
Not sure what it could be.....

Im ganna be doing a 3" lift soon with a AAL in the rear, maybe I should see if that gets rid of it?

 

Could be a bad u-joint. Does it happen when you take your foot off the gas ?

 

Yep, it doesnt matter what I do it still does it, brake, no brake, excell or put it in neutral. Its still there.

Thanks for the response man!
I will look at the U-joints just incase..

 

The only thing I can think it would be is u-joint problem, or too much slack in the CB but theres not.
Maybe my LSD?
I did just change the fluid to RedLine LSD fluid 75-90..... But it did it before that slightly, so Im not sure. I might just have my local machanic to diagnose is, and check my u-joints....

 

Ive been reading throug some threads and apparently these 07's are known for the shudder/vibe. Alot of guys have it, and there isnt really a fix. One guy said his went away after he put a lift and bigger tires on. So Im just ganna wait until I get my lift and tires on, and then see what kinda vibes a have.
And what really sucks is that Im a LB and no one makes a one piece drive shaft for the DC LB....
Thats what cured my 02's vibes.