I think you can find good Mexican food anywhere there is a decent population of Mexicans? I do think there are plenty bad "Mexican" spots in Texas, but I think it's fairly easy to differentiate between a place that's legit and those that serve food someone from Minnesota would enjoy.

I've also never taken any of my girlfriends (Mexican) friends or family to a tex-mex place, and them not be over the moon. Though they do become worried for Americans health imagining we eat like that regularly. I also personally differentiate tex-mex from what I call white people Mexican food, idk exactly how to detail the difference but if you know, you know.