The whole cab shimmy shakes when slamming the door shut.
It seems natural with the added cab length and no vertical supports. Is it?

 

The back passeger door on my scab makes a loud noise when opening, and has to shut pretty hard to avoid haveing a rattle while driving. Seem to close completely, but doesn't seem aligned as well as the other one.
Also, speeking of the cab shaking. While interstate driving 75 or so the passenger seat shakes like heck when nobody is in it.

 

My passenger seat shakes pretty good when I hit a bump or something, and I have a single cab. I think that's something to do with what they used to attach the back of the seat to the bottom, because only the back shakes.