Oklahoma City to Palm Springs Ca. In February best route???

We are in Phoenix right now. We got here yesterday from Denver via I-10, not I-40, because temperatures along I-40 were in the teens at night compared to the 30s along I-10. When you are stopping along your route for several nights, that is a major difference unless you have much better RV insulation than we have. And when we had rain on our route, Flagstaff had snow (the elevation of Flagstaff is 7,000').

So I would definitely follow the I-20/I-10 route recommended by the others.