Firstly you don't say where in Texas however you mention Phoenix and LA both of which I 10 would have to be your choice and or you mention Barstow which would best be reached by using I 40. If your overall goal is to avoid LA and the grapevine I 40 to Barstow and on to Bakersfield avoids both with good roads and little weather issues. And out of Bakersfield use a sometimes rough state hwy 99 north. That time of year stay on top of weather conditions...that is what keeps you out of having weather related issues. If your starting in the Dallas/Fort Worth area use US 287 to Amarillo and use I 40 west. US 287 is a much under appreciated highway, but it's the best if Barstow/Bakersfield is a destination.
