You must declare all grades to AMCAS. They will figure a undergrad, post-bac, and graduate GPA for you. Then you will get a composite, undergrad+post-bac, GPA.
Most adcoms will look for a positive trend and thus you need to ace every post bac class. Its the only way. It would take tons of credits to bring an undergrad GPA over 3.0.
Finally, and perhaps most importantly, you must do well on the MCAT. This means you have to get 30 or greater or you will be limited.
Good luck.