Ok, I know this has been posted about probably a few thousand times, but I am at my wits end. This dishwasher will not work right. The top rack arm is not spinning at all. I have replaced the chopper and screen, the circulation pump, everything is spotless, no clogs in any of the piping going up the back. If I tape over the holes on the bottom spinner, the top spins like crazy. What could I be missing? I'm so disappointed, I don't know what else to do.