Here's the van being hauled onto the tow truck with Matt in the foreground. I had assumed that the problem was the transmission -- which we have already arranged to replace -- but it seems it is not so simple. Matt did some basic troubleshooting on the spot with the voltmeter, and was able to find that there was power all the way to the motor (that is, the problem didn't lie between the batteries and the controller).
Back went the van to Bill's for more diagnostic testing. Everything indicated that the motor seemed to be the issue. Here he is prepared to disassemble the motor from the transaxle for a final test.
Bill took a peek inside. He found that the 6 springs that push down on the brushes may have been installed incorrectly. They are pushing the side instead of directly on the brush.
We checked EVA's manual for our EV and nowhere does it specify that we should check inside the motor before installing it! Of course all motors are tested before they're sold, and this one has about 100 miles on it ... but though quite unusual, it's not unheard of for electric motors to be defective.
Next, we'll have to find a way to get this motor back to the manufacturer for further testing. Stay tuned!