I'm curious - you said you had 3 wire romex connecting the two 3-ways. Have you considered the possibility of induced voltage? I know this caught me a couple of times early on in the trade - I would measure about 30 (induced) volts on the not-in-use traveller of a 3-wire in a 3-way configuration (in new housing, properly wired). 55 volts is a higher number than I remember ever seeing, but maybe a possibility, or at least part of the puzzle?
