GE Dishwasher PDT750 Circulator pump not working when fill, working when empty

[mookie3333]

I've been trying to troubleshoot this for over a week.  I suddenly noticed my dishes were still dirty after a cycle.  Ran some tests and noticed that the circulation pump was starting briefly (2-3 seconds), then would cut off.  This happened over and over again, throughout the entire wash cycle.  I assumed it was cutting off on thermal protection and that something may have been blocking the impeller.  Opened up the circulation to find some crud in there, and a small stone, thinking the stone caused the problem.  Reassembled everything, and same symptom still persists.  Circulator on for 2-3 seconds, then off, over and over and over again.

I then pulled off the diverter adapter plate and noticed that in Service mode on circulation setting, the diverter is working properly, switching between the 3 outlets every 30 seconds or so, but the pump would still power on for 2-3 seconds, then shut.  I would pull open the door quickly to notice water shooting out of the diverter, so I know there's no blockage.  

Funny thing is, if I drain everything (drain pump works fine, no issues), and run the circulator DRY in service mode, it kicks right up, no issues.  No thermal shutdown after 2-3 seconds, nothing.  So, I tried something.  I opened the door and just threw a cup of water in the tub and ran the circulator in service mode.  Circulator runs fine, no shutdown.  Threw a second cup in, and resumed the test.  Again, runs fine, no shutdown.  Third cup, the water level comes just about to the top of the sump.  Tried to resume test, and now the circulator is shutting down after 2-3 seconds again!  

What gives?? Anyone have any recommendations?  Could this be related to some sensor?  I don't think the turbidity sensor would do this.  Any help is greatly appreciated. Thanks.