I have a steel cyclocross bike which doubles as my weekend bike and my daily commuter. About a month ago I got in a wreck and bent the rear derailleur hanger and the rear derailleur. Got the hanger re-aligned and put on a new derailleur. Chain was not all that worn (checked it) so didn't replace it.
Fast-forward about three weeks. I was noticing significant "phantom shifting" which was primarily when putting a lot of torque on the pedals (I have 220mm cranks and go up a 10% grade on the way to work). Everything seemed to be lined up on the stand, but on inspection the chain had multiple links with cracks in them. New chain=problem solved... for about 3 days. Now it's started acting the same way. It frequently "skips" and occasionally tries to shift from the middle chainring to the small chainring if I'm riding uphill, which threatened to unhorse me once. It can also do this on the large chainring. I checked visually and there's no snaggletooth. The chainring does seem to have a very minor wobble -- less than 1mm left/right, but I've noticed that the phantom shift/skip is indepenendent of where my feet are (ie can happen with left foot up, right foot up, etc)
Any ideas on what else could be causing this / what should I check?