The answer is yes, but IIRC (and I might err) slavery itself wasn't a factor in the economy, or even society (unless you count the Spanish/Mexican versions).
Texas had horses, cows, and cotton, it was a major trade center for the South (and sold to the north as well) until the very end of the war. Then it gave birth to much of the post war cowboy mythology because all those famous trails started there.
While you are right, that I did a poor job of phasing my question, it was not that I wanted to know if Texas had been a “slave state”, I knew it was. My question would have been better asked as: ‘Was Texas a major Cotton producer pre-Civil War?’ It was more about economy and employmet in Texas, than about slavery, per se. I just didn’t think that cotton was produced in great amounts in Texas before there was suitable transportation routes developed to get the cotton crops to market. Unlike the SE & SC areas that had easy river and ocean/Gulf access to shipping.