I have similar stats as you, kind of. I have cGPA 3.45 and sGPA 3.07, and I also plan to take the MCAT in spring '16. What I am doing is retaking science classes that I got C, which are 3 classes, and plan on taking biochem and genetics as well as upper div science classes. I chose the DIY postbacc route because it is cheaper and it actually raises both your GPAs tremendously. Also, I have read and heard from different people that doing a formal postbacc program and not doing well in it will shoot your chances of getting an acceptance anywhere, because it shows adcoms that you can't handle med school classes. So if you have the money and you can guarantee you'll do great in the postbacc program then go for it, otherwise don't.