The first thing I would check in such situation is the drive block.
Remove the agitator and the spanner nut. Visually inspect the drive block. If it has to be replaced you will have to remove the cabinet and the inner tub.
In order to remove the spanner nut you will need a special spanner wrench.
- The part number for the spanner wrench
AP3538707
- The part number for the drive block
AP2905773
The drive block
Gene.