whoa! maybe some one can help me out here.. i have a 2000 silverado ls with a long bed. its an ex-work truck that i picked up cheap. the problem is that it shakes at highway speeds. at about 65mph the pasanger seat visibly shakes and you can feel it through the whole cab. i had the wheels ballanced, i had a front end allingment, i switched the wheels thinking that maybe one was bent, i got new tires thinking one might be "cupped" (and they were worn out anyway). i cant figure it. it seems to be coming from the rear of the truck. should i replace suspension components? also, the bed sags towards the drivers side. this seems to be a problem with a lot of chevys. whats up with that? someone help me out please?