Well I can tell you from my experience as a med student at Mayo, in terms of your "will my undergrad GPA kill me?" question, I don't think it will here. Mayo doesn't have a GPA screen (they do have an MCAT screen), so your application will at least get looked at and your personal statement will be read. again in my experience (also applied with a high MCAT/low GPA with an upward trend), the admissions committee here is very holistic and can be quite forgiving when it comes to poor grades in the past. The rest of your application is very impressive and it sounds like you explain your undergrad GPA in your personal statement. I also agree with Faha that the older clinical volunteering is definitely still important.