I also have a bad vibration issue at above 50mph under load coasting or in neutral pretty much disappears from all searchs I did on this subject and under car inspection when I lift up on driveshaft right at rear of trans I have at least 1/4" of up and down movement my flex joints look good front and back car has 265 to 300,000 on it I am thinking it is either the u joint or the center driveshaft carrier which I do not see either? Is the center carrier under the heat shield midway from front to back? I am hoping that is what is causing the vibration and is a fairly simple fix. I find this site very helpful with keeping this 30 yr. Old car on the road.