guys, my 2010 STX that I just picked up has Pirelli Scorpion STR 285/45 R22 tires on it. horrible in the snow but after 2 balances and alignment the truck still shakes and vibrates at highway speeds.

the passenger seat shakes like crazy. a little annoying. and after doing some research it looks like it could be these tires causing this problem. how would a tire cause this? just curious. it's not my specialty by any means.

has anyone had this trouble with the Scorpions and did replacing them solve the problem? thanks fellas