[acaskie]

When I had a similar problem in a '66 Shelby Mustang with a 4-spd Toploader, it turned out to be an out-of-balance driveshaft. Of course the thing was about four and a half feet long. How an eight-inch driveshaft can get too far out of balance is a stumper, but I suppose it's possible. I would bet its the U-joints as well. --