I received the new vent assembly yesterday and installed it this morning. I have run a one hour wash cycle and the dishwasher worked perfectly. So, it appears that the culprit was the vent fan within the vent assembly. The problem is resolved. Many thanks.
Also, thanks bigbuck for the suggestion to disconnect the fan before running diagnostics. That suggestion was certainly key to finding and fixing the problem.
I appreciate all of the help. And my wife is very happy to have her dishwasher back. Woohoo.