DH was suggesting that the magnets may be weak. It's something worth checking, but I'm not sure how at this point.
Mechanically, or electrically, as I understand it, any motor will slow down or stop with too much load. Just as a gas engine loses horsepower as it gets older and "worn out", I expect the electrical motors to be the same. I just have to figure out which parts correspond to "horsepower".
My goal here is to figure out why "normal" is too much. I'd hate to have to bin the 3 motors, and possibly write off the 730 at the same time.
I will definitely report back. I got caught up with a client today, and have a meeting this evening, but if I still have some energy tonight I'll do what Joe suggested and see what happens. Otherwise, tomorrow's completely free from what I can tell.
I'm going to go scrounge up some 600 grit sandpaper out of the black hole DH calls a garage.