Video showing how the Dynamic Wash System spray arm is designed to operate.

I was hoping you would see my comment dadoes. That answered the question for me. I read the pump could be the issue, and since I am not you, I will have to leave it to a professional and hope he will properly diagnose it and charge me accordingly.

Try cleaning the filter as described in the Quick Start Guide.

The manufacturer's spray arm part number is W10860176. According to PartSelect:

1. Our research shows that by far the most common reason why your spray arms may not be spinning properly [which would lead to poor washing performance] is the build-up of dirt and debris. Remove the dishwasher basket to freely access the spray arms and carefully clean them out.
2. Under the Spray Arm there is a Nut. To remove the Lower Spray Arm turn the nut 1/4 of a turn counter clockwise. You can then lift the Arm off...
3. If this does not resolve the issue replace the arm.

My sister has a Kenmore dishwasher that was performing terribly. The wash arms were filled with debris that blocked most of their holes. Once the debris was cleaned out, the dishwasher performed well.

Thanks wdc. I have routinely cleaned the filter. I can't find the nut just by feel, so I will spend some more time trying to find it. I had seen a vid that showed how to easily take off the entire lower arm, but I could not get it it to easily disengage, and I did not want to force it. I took a toothpick yesterday and put it in some of the holes to see if I got any matter from them. I'll mess with the lower arm a bit more. I would like to save a few hundred dollars in service cost if I can.

The PartSelect instructions were wrong; there's no nut. Watch this video to see how to remove the wash arm:

KitchenAid Dishwasher Lower Wash Arm Replacement W10860176

BUT be sure the read the third and first comments for instructions on how to reinstall the wash arm.

The first commenter replaced his spray arm with the simple W11101428 which you can find on ebay for $20.