I would questions your figures and facts. If you are speaking of native-born Texans of Mexican decent, I might agree they speak English - but as their 'only' language, that has not been my experience with them.
I don't know about 60% being 3rd generation - if that is true today, it will not be in just a short time. Texas is being deluged by illegals. We have possibly not reached the level of California, but we are not far behind. You are correct in that there are many, many Americans-Texans of Mexican decent that have been our family, friends and neighbors, but they are growing old as many of us and how long before the new generation realizes, they can demand and get more and more. As Isaid, I question your figures, respectfully, but also your post made it sound as if Texas was not in a critical state - when it is. Our cities are broke and our state is in a very bad financial state. We have a high sales tax and extremely high property (school) tax. The reason for this, I believe, is caused by the influx of illegals draining the social services, law enforcement and schools. When you have that many people migrate who are unable, or unwilling, or just not required to pay for the services they receive, it has to cause problems. It is already and will be even more frightening in the future.
As I said, it may not be as critical as California, but it is not a rosy picture. It is certainly having a detrimental effect on cities and is changing the culture of even small towns.
I wouldn't even compare them because they aren't the same people --at least not around here. For one around here it's a big mistake to refer to a SW Hispanic as a Mexican because Mexicans are citizens of a foreign country and you'd be corrected immediately. They used to let you get by with calling them Mexicans but with the current invasion of people from that country, most lately call themselves Spanish or Spanish-American Indian or Hispanic or New Mexican. Even those descended from people who left Mexico almost a century ago are quite a lot different than those who left yesterday.