Changing a grade from an A- to an A by retaking a whole class is way more effort than it's worth. And your PTCAS pre-req GPA doesn't matter too much, each school will calculate a pre-req GPA that they will use in their ranking of applicants, based on their specific pre-reqs.
You need to find out what each school's grade replacement policies are regarding retakes. If you are in a position of applying to schools where you will have a pre-req GPA of 3.6 you really don't need any further retakes. If the rest of your application is solid a 3.6 will work.
If there are schools where you will have a 3.0, your chances would be slim. Do your research and narrow down your list of target schools to the ones where your GPA will be the highest in their calculation. Applying to well-selected schools will be a lot more time and cost-efficient than retaking classes will be, especially retaking an A-. You should be able to do the math and see what kind of effect this would have on your GPA (and you will find that the effect is likely only a couple hundreths of a point). Excel is your friend, my friend.