I just went through this problem and fixed it.
First, disconnect the shift cable at the reverse bucket. It's a cotter pin/washer on the right-hand side. Then try moving the bucket up and down manually. It should flop up and down easily. If it takes effort, that is the problem. See my recent post regarding how I fixed it. It involves removing the pivot bolts and bushings, and sanding out the hole under the bushings. It shifts like butter now.
Mike