When i release my clutch and dont give much gas, the whole truck shakes. The videos dont do it justice, but it shakes the whole truck. With new and old transmission mounts it still shakes. And as you can see the drive shaft is having a melt down. My motor mounts look decnt and the trucks on its second clutch. Im not sure if this is related to my  hydraulic clutch being very stiff and releasing at the very top. Also you can feel the pedal vibrates a bit when you just rest you foot a tiny amount. Maybe my clutch is contaminated with oil as my rear main seal leaks pretty bad. I cant really creep what so ever without the truck shaking so its either launch or shake the whole truck. Im not sure what would cause this. The truck only has 95,500 miles and its a 1990 c3500 with the 454 and the sm456  4speed transmission. Also the truck did mostly heaving hauling for a good amount of those miles.