Chase, I am from OK also and I consider myself Southern. OK has been a state for 100 years in 2007. Before that, it was Indian Territory and was populated by Indians except for some white intruders. Not all Indians lived in OK. My Indian ancestors gave up their tribal membership and lived in South Texas. A lot of whites who came to OK 100 years ago and since came from the Southernmost states and you don't lose your "Southerness" in 100 years. I know my family didn't. Now that I think about it, I am the first generation to be born in OK. I am not quite 100, but close.
I am sure you know all this history, but this explains why we consider ourselves Southern.