If you check a couple of the websites you'll see that the Freshman retention rate at Duke is about 97 - 98%. That means that if there are about 1600 Freshman, about 40 -50 of them won't be there as Sophomores. So that is the number of spots for transfer students. Probably around 700 - 800 transfer applications come from good students at other schools - a lot of those are from kids who were waitlisted at Duke or just barely missed making the cut. Your chances of getting in as a transfer student, by that calculation, are about 1 in 15 (that is, if you have good grades as a Freshman at another competitive school).
What makes you think that your grades at Auburn are going to be so much better than your HS grades? Or that you will be able to out-compete your rivals as a Freshman when you didnt beat them in HS?
A better plan, in my opinion, would be to try to find a school that is a good match for your credentials, and then to commit yourself to having a great education at that school.
Duke is a wonderful place, and the kids who go there get a terrific experience, but it is not the only great school, and it is not for everyone! And, if you transfer in as a Sophomore you are going to miss one of the main things that is unique about Duke - the Freshman Campus experience. So, I think there are some major flaws in your plan. Better to just find your match and go with it .....