Fast Spin Intermittent on Front Load Washer?

My machine quit spinning fast. It gets to six minutes left in a cycle and then shuts off. I got error code 47. The guide said for that error code to replace the door lock. I replaced the door lock right away and it worked one time and then had the same problem. The next thing the guide said was to replace the main control board. I waited nearly a month for the part then put it in. I thought that fixed the problem. The machine worked just fine and spun for 4 loads and then experienced the same problem again.

I think maybe it's the belt? I think the belt maybe is stretched and then it shrinks a little when the machine is not used for a while. I think since the machine was not used for over a month this time it shrunk enough to do several loads before stretching out again.

I just put the machine into test mode while empty and no errors came up. I loaded my machine with wet clothes put it in test mode and it spun for a bit, but shook a lot and then threw error 55 "under speed". The tests for that involve the motor, bearings, and motor control board. I'm still thinking it might just be a loose belt as there were no errors when I ran the test mode with the machine empty and the machine did spin just fine for 4 loads after I replaced the main board before it stopped working again.

Machine is a Crosely (Frigidaire) cfw47000LWO (that is the letter O on the end).