Actually Tulsa makes a lot of sense in the CUSA because Tulsa is an oil town. There are a lot of ties with Texas because of the economy.
And while I agree with you about Ft. Worth being west and San Antonio southwestern, Dallas is about as south as you can get among big Texas cities. I once heard someone say its hard to find two major cities more alike than Atlanta and Dallas. Dallas and east Texas originally were dominated by immigration from the old south, but Houston, being a port city and an oil capital is much more diverse. Culturally, in many ways it is much more western than southern, even if it is geographically close to the south.
With Houston's immigrant mix of Mexicans, Central Americans, Indians, Pakistanis, Nigerians, Italians, Greeks, Chinese & Vietnamese along with southerners and midwesterners, its not much like the old south. The southern accent is much milder than just about any other region of Texas east of Interstate 35. A few weeks ago I walked into a Toys R Us in central Houston. The first language I heard was Russian. The 2nd was Spanish. The 3rd was Chinese. After hearing a couple of English speakers, the next was a Muslim lady speaking a language I was not familiar with, probably either Urdu or Arabic. As I was checking about a Hindu lady behind me was speaking an Asian Indian language. About the only thing missing was Vietnamese (after LA, Houston has the largest Vietnamese population outside Viet Nam). While that might be common in the old south in 20 or 30 years, its not the case now.
Dude - I do not think that Atlanta and Dallas are anything at all alike - Dallas is heads above - never felt safe in Atlanta - as far as Atlanta being southern, most of the people I met there were from the northeast - Arkansan