Kitchenaide Dishwasher Upper Arm Problem

When checking out a poor cleaning problem on the upper tray, I found that the upper arm was not turning.  A repairman came out and replaced the filter and a valve, but the upper arm still doesn't turn.  The upper arm ports have no obstructions and the arm moves freely to the touch.   With the door slightly open and pushing in the door shutoff switch, I observed a weak flow through the upper arm ports, which was not enough to move the arm or do any cleaning.
The repairman is saying there is nothing more he can do.  However, couldn't this be caused by poor pump performance?  Any recommendations?
Bob