It's really hard to give actionable advice without seeing your site, but if you feel confident that your content is all in order, I would put some focus on the UI / technical elements of the site.
I wouldn't presume to know which user metrics Google monitors, but I do believe that some of them are part of Panda (personally, I doubt bounce rate is important at all, but some kind of long click vs. short click ratio could certainly be a factor). Are people sticking around?
Second, don't confuse Panda with Penguin. If the dates match up and you've definitely been hit by Panda, disavowing links probably won't help you at all.