You can save totally 400miles/7hours if:

You can save 120 miles if you don't tour New Mexico. And if you don't tour Austin and vist San Antonio before McAllen, you can save another 85 miles. There isn't much to see in Austin, except for the state capital and some hills/lake in the east. It is just not comparable to other places on your way.

The route I ploted has a total of 2850 miles, 400miles/7hours less than yours.