I don't like giving up on a difficulty. I went back down to the Allegheny and checked that diver rods were properly secured. As I tilted the engine to the side, a fiber washer fell out of the front drive train.
I am not sure if it is an extra part that fell into the gears (How?) or a end washer for the driver worm gear. I included a picture. The washer is not plastic, but a compacted fiber.
The engine still slows and drags at Speed Step "23". It also will stop and make a rapid machine gun "tat, tat, tat" out of the sound systems.
Maybe if I shake the engine upside-down, more parts will fall out.
Sincerely, John Rowlen