Shaking over rough roads/bumps

[81GMCSierra1500]

Hey!

I'm just narrowing down on little issues (finally through all the major stuff, yay!) but one thing sticks out like a sore thumb... it shakes like a leaf over rough roads or bumps, it's not just like a front end wobble, the whole frame "wiggles" over rougher roads, it's mainly felt everywhere, except in the steering wheel... I've got a hunch it's something wrong with the rear suspension... Shocks? broken leaf spring? What are y'all's thoughts?