After some reading around and looking at my shoes DH and I suspect that my issues with my left pedal could be shoe-related. Because my left leg seems to be a bit shorter than my right (I have ALL of the telltale symptoms...I tend to list off to the left a bit on my saddle and every niggling running issue I've ever had is on my right side, since the longer leg ends up working harder) I place that cleat a bit forward of my right cleat.

This is a photo of the underside of the same model of shoe I have:

On either side of the right cleat there is a divot in the tread (just behind the ball of my foot), so the pedal doesn't end up rubbing on the tread in any way. But on my left shoe the cleat sits (directly under the ball of my foot) where there is no divot on the sides AND there are obvious gouges on the tread around the cleat on the left shoe. So we just took a utility knife to those spots to knock them down a bit. Hopefully that will solve the issue. I'm really tired of feeling like I've been on the losing end of a fight after riding, heh.