2000 T2000 rear cabin shakes.

i have 2005 volvo i am sick of it it keep shaking while driving as soon as it starts pulling it shakes even more it vibrates while driving my dashboard it looks like it is going to fall out stearing wheel shakes i done everything on front end new tires even new wheels ,shocks,checked axel,king pins,air bags,drive shaft,every thing seems to be normal,had balance done alingment and freaking peace of crap volvo still vibrates while driving whole cabin it feels like its gonna break off,,does anyone else have this kind of problem please help ,i even replaced fifth wheel thinking it might be because of that but no.please any body know what might be