van rides hard....struts?

I'm hoping somebody here can help me on this one. I had the struts replaced all the way around the vehicle July 2003 and now when I'm driving it it feels like I'm driving on rails. when I drive over the bridges tracks and other nasty bumps it now slams them unlike a year ago today but my wife brought the vehicle back to Sears and they say it's not the struts.... any ideas?

Thanks!

if u got white ones they are cheap. the yellow ones are the heavy duty ones.