Another Texan here. Galveston is indeed shit, though I think you already dropped that from your list.
Generally speaking, Texas will be a lot more pleasant outside of summer. Yeah, it seems obvious, but it'll be more fun if you plan to be here in fall/winter/spring than if you come in July.
Austin's a great city, but it is pretty distinct from the rest of Texas. If you can time it right, there are two big music festivals (SXSW and ACL), but figure out tickets/etc ahead of time, or just come whenever, there's always plenty of music playing and stuff to do.
I'd say visit Austin, get BBQ at Snow's (show up early, ideally before 11am), and go camping in Big Bend.
Also, ignore
>>323270 - Wisconsin has some really boring parts, but Madison and Milwaukee are both great cities (Madison's a lot like Austin, including being pretty distinct from the rest of the state, more liberal/hippie.)