I'm with nomercy - you were probably looking at a coyote or hybrid. The other distinct possibility in Texas is that you were looking at a domesticated wolf or wolf/dog hybrid. Texas is notorious for road side zoos and these animals are often let go when the show goes belly up. These dogs get out and can really cause some damage. I would think it highly unusual for a Mexican wolf to cross your path - but it could be possible. Just not the most likely.