About how old is the unit?
Have you done heavy (overloaded) loads?
Make sure if you have a speed switch it is on fast.
4 yrs old and knowing my wife yes overloads
It is likely going to be the clutch. When you get the cabinet off check to make sure there is nothing inbetween the tubs. I have included a video on how to remove the cabinet and one on how to change the coupling. The last one is just to get down the the transmission. To remove the transmission remove the dispenser from the agitator and remove the bolt in the bottom. There maybe on more cover under the dispenser. Pull the agitator out by its bottom. Remove the other three 1/2" bolt from the bottom of the tranny and slide it out. From here replace the clutch.
Click here for the cabinet video