I agree, your stops are well planned. Still a lot of driving. Use lower gear driving the mountains east of San Diego also down hill and avoid using your breaks all the time.
You also will find a border patrol check point before Las Cruces NM. Instead Fort Stockton you could stay at Balmorhea SP. Often overlooked and an oasis in the harsh lands http://www.tpwd.state.tx.us/spdest/f...rks/balmorhea/ just a very short distance off the interstate.
The I20 stretch to Junction is 80mph. Don't speed because highway patrol is waiting for you. I knew about this but still got a ticket only doing 8 miles over the speedlimit.
Fredericksburg TX is a nice town on your way to Austin.
I like I8 with the mountain drive, the farmlands, the sanddunes and the low desert. Gila Bend has lots of options for fast food and Benson is a good place to spend the night.
Yeehaw