I tried the capacitor. No difference in performance.
I also played a bit more with the engines. I tried just a single GP9. It worked the same as if I double headed it with it matching A unit. The red light does not flash on the GP9s (by themselves) but they do not run right. Jerky & surging.
The GG1 by itself gets the red light flashing and when it surges - it really takes off.
I tried the Pennsy Torpedo by itself. At speed step 1 it took off at a good clip and ran jerky. ZW-L red light did not flash. Drop the voltage down to 16 volts. The torpedo then started to move at speed steep 6 instead of 1. Nice and slow and smooth.
Unrelated to the red light flashing: I dialed up the power on channel 1 (tr 1 on the legacy remote). I wanted to cut the power so I pressed the direction button on the remote to cut the power - when I did that, the light on the amp gauge went out. It turned itself back on after a few seconds (and I was still holding the button down on the legacy remote). Only channel 1 does this. The power remained off on the channel until I release the button on the remote - which was correct. I tried this on the other channels and the lights do not go off for any other channel when I press the direction button down. At least this oddity does not affect any performance.