I am having this ongoing issue that the passenger seat will vibrate front to back rapidly while on the highway. I recently got all my suspension checked, replaced rear upper control arms, got 20" 87s roadforced balance on a hunter gsp9700. This happens on my winter wheels and my summer wheels, but it is considerbly worse on the 20" because of the weight im guessing.

What could be causing this? It must be something in the rear of the suv, something suspension related? Bushing?

Any ideas? Thanks!