GE Spacemaker spin cycle problems

I just inherited a "new" old washing machine from the upstairs neighbour. It worked great at first, but I am starting to have problems with the spin cycle.

When I put it on spin the agitator twists up all the clothes so that they are wrapped around the agitator or else bunched up on one side. Then the drum starts turning, and, of course, it is imbalanced, so it stops spinning and gives an imbalance signal. It's a top load washing machine. Any ideas?

Correction: The model number is: gsls1100d

Edit: I think it may have to do with the stupid load sensing function. The agitator turns to determine the load size first.

Edit again: the levelling locks described in the owners manual are not there.