My 1977 Chevy trucks has a problem that has become worse over the years and I need to figure out how to fix it now because it is getting much worse.

It has a 3 on the tree Muncie transmission. When I put it in reverse it shudders and vibrates like crazy. The entire truck vibrates. If I backup a hill I have to slip the clutch slightly so I can move it. With the entire clutch fully engaged it feels like the entire drive it about to fall off. In forward gears there is not a single problem.

Any ideas would be very much apprciated. - Tom