I live in Colorado Springs and often drive to south Texas. I go through Amarillo.
If I were going to OKC and just wanted to get there I would:
- Drive I25 to Raton, NM
- At Raton I would take US 87 to Amarillo through Dumas
- At Amarillo I would get on I40 to OKC!
This shows on google maps to be about 9 and 1/2 hours. It isn't interstate all the way but it is 4 lane (minimum) divided highway all the way.
I might go another way if I wanted to sight see!