How should I troubleshoot a dishwasher that stops in the last minute of the cycle?
What you might have is a loose wire in the front panel ; this appears to be a common problem with Vario Motor errors on the LG Washers.

Verify that the motor turns and does not have any rough spots or stiff spots, check your sump and impeller areas again to be sure - but you are likely looking at a loose wire in the front panel.
Apparently the cables get stuck on something in the door panel and lose their flexibility and get pulled loose or apart - or wiggle to an internal breakage (this happens when the door is opened and closed). 

The other possibility could also be the main board.