If you felt resistance in the impeller and then it turned freely after the first turn or so then you may still have a problem with the impeller or the motor that drives it.
The resistance of the impeller should be consistent at any point in either direction.
Try this; try spinning the impeller both directions. Spin it more than a few times all the way around, both ways. Do that a couple times to be sure that it doesn't again become harder to turn.
If it does then again further disassembly will be needed to determine what is causing the resistance.
If the motor is having to drive the impeller with resistance applied to it then the lower speed of the impeller turning will greatly reduce the amount of water pressure sent to the spray arms. This will seriously impact the ability of the unit to clean the table ware on the top rack while still doing a good job on the lower rack.
If it checks out as good then run the unit for as long as it takes to fill it and begin the wash cycle. Stop the cycle and set it to drain the water and turn off. This will warm up the components and may show something.
Once again check the impeller. If it is free then it should be ok. The first time may have been a coincidence. If you again feel resistance and then a freeing of the impeller something isn't right. Further disassembly will be needed to accurately diagnose the unit.
Please let me know what you come up with.
Edited by The Home Smithy on 5/1/2010 at 7:13 PM EST