Since you seem to be looking at all the right venue, I will just throw in few more perspective.
1) It could be that your body is overcompensating for issue on your left side...
2) What kind of pedal system are you using? Try platform for short? Compared to using clipless, this will get rid of any potential issues you might have with foot angle, cleat position, etc. Also, it's definitely something cheap (or even free) to try out. Maybe using your most comfortable tennis shoes with platform to see if it changes dynamics. (could be partial solution to #1 too)