I guess it depends on what type of post-bacc you plan to do. You can take one at a medical school to prove your worth and do well to almost guarantee admission to make up for prior bad grades. Where I went to medical school, if you did well in their post bacc program (one year) then your admission was 95% guaranteed.
Now, if you do your own post-bacc which is what I did then those most recent classes take the place of the undergrad ones. True, you still have to report all classes you have ever taken but if you take all the pre-req's and do really well then the prior classes are really a moot point. I had very poor undergrad GPA (2.7) with science GPA of 2.5. I went back 4 years later and took Chem I/II w/lab, Organic I/II, Organic lab, Physics I/II w/lab, and biochem all at the same time over the course of the year and worked a 32 hour week at the hospital. I came out of that year with a 3.8 GPA thus proving that I could do the work and not falter under the heavy load.
What medical schools are looking for is someone who isn't going to quit in the middle of things because they are overwhelmed with the material. The first semester of med school is equivalent to 35 credit hours and each semester increases in credits.
This strategy worked for me. I will be an attending here in 2 weeks. Good luck and I hope that answered your question.