When I moved to Houston in 1969, as a Democrat from Chicago, there was only one Republican that held a state wide office, and he was a drunk.. LBJ presidency changed all that, and changed the state to solid Republican within 6 years to solid red, from then on..
I was still a holdout until I served as Chief of Protocol for a Democrat Governor in 1972, and was an insider behind the scenes, and saw too much to ever vote for them again..
I quit that cushy post within the first year because I could not stand the things that I saw and was asked to participate.. They were and still are despicable people indeed..
It wasn't quite that neat and sudden, for instance in 1976 Texas voted democrat for president. In 1968 after Johnson, Texas voted democrat for president.
Other offices took a long time to become republican, for instance in 1993 when the GOP took the other senate seat. Rick Perry himself worked on the Gore campaign and didn't switch parties until late 1989.