Could be the motor /inverter assembly or possibly the mode shifter hub under the tub. GE apparently has issues with this machine. Only by using the mini-manual inside the machine would a technician (or you) be able to tell which it was. We can't walk you thru something like this since we are not there to check voltages, etc. This info should be inside the console or taped to the inner cabinet somewhere.
I will say that from other forums topics I have read, this machine has trouble with the motor/inverter more often than anything else. Changing the belt is also more strenuous than on previous GE toploaders.