My Maytag Stack washer will spin just fine, but the agitation has been slowing down for awhile now - with a squealing sound when it tries to agitate. It might move an inch or two in either direction, but that's about it.

The belts are new, and the transmission wheel on the bottom of the washer can be turned by hand. The drum spins normally. It is only the agitation cycle that doesn't work.

Can you advise as to what might be wrong, and what parts I need to fix it? Thank you!