Doooh, you can make it there by road in two days. I would highly recommend staying in Albuquerque the first night if you are headed for Dallas/Ft Worth. SD to ABQ is 11-12 hrs drive. In the summer, the motor lodges in ABQ are usually all full so you will have to book in advance. The next day, ABQ to DFW will be about 8 hrs. drive.
If you are driving to Austin/San Antonio, stay the night in Las Cruces, NM or El Paso, TX (however far you think you want to go). This drive is 10-12 hours from SD. The next day will be 12-13 hrs drive to Austin/San Antonio. The west TX stretch of I-10 moves fairly fast, as I recall.
I think it is nice to have your own vehicle there and not be hamstrung by airline luggage regulations.
