Impeller kit?
What is the part number of that kit?
Sometimes the food chopper screen gets plugged up with stuff.
If the screen gets plugged up you should replace the food chopper.
A plugged up screen will cut down on the pump pressure and the top spray arm will suffer first.
Take a look at this video. This is a whirlpool dishwasher, but kitchen aid is made by whirlpool so it's the same.
Video: Whirlpool Dishwasher - Check for foreign objects in food chopper