Some Texans speak with slurring "s" sounds, sometimes making a soft rasp or even a "sh" sound? example "Shtudent" instead of "student". Is this traditional or a new affectation?
This phenomenon is called s-backing, s-retraction, or s-palatalisation, because the speaker is moving their tongue further back in their mouth. As Ben Yagoda points out in Lingua Franca, and as noted in another EL&U Stack Exchange question, American speakers commonly employ an /sh/ sound when saying a word like "grocery." Other common shifts include using /sh/ at the start of the word (as Sean Connery does) or, specifically, using /sh/ in the combination "str-" (e.g. strength).
The phenomenon is more widespread than Texas, and has occurred at a greater rate in the last 70 or so years. Linguists Olivier Glain and Jean Monnet (2014) connect s-backing (or, as they call it, palatalisation) to post-World War II changes including the decline of Received Pronunciation in the UK and a similar democratization of accent in the US. They find an increasing level of palatalisation among Scottish and American speakers. In the specific context of Philadelphia, Duna Gylfadottir (2015) found that the /s/ sound in "str-" has turned to /sh/ more frequently over time.
The research is ongoing; a 2019 paper by Jane Suart-Smith et al. find that the specific shift in "str-" words occurs in corpuses representing the American Midwest, South, and Canada, but not in the American West. In any case, so far results suggest that the phenomenon is broader than Texas.