If you are interested...I would recommend doing a rotation at one of them (I would recommend either UT Southwestern/Parkland or Texas Tech). Also, from what I understand, UTHSC San Antonio will be add 2 civilian EM spots to the combined Army/Air Force Program at Brooke Army Medical Center - Fort Sam Houston (BAMC), Wilford Hall - Lackland AFB, and University Hospital. I would imagine this program will be very competitive with only 2 civilian spots.
I agree UT Southwestern is the most competitive in Texas, followed closely bu Texas A&M - Scott & White. Tesas Tech is good, but I think their location is a draw back for some, if not many applicants. UT Houston definitely is the least competitive in Texas...for now. They have a new PD who used to be assitand residency director at Cook County in Chicago - and he will probably establish UT Houston as a very respected and competitive program.
If you have only average grades or board scores...definitely do a rotation at one of the places you want to go to the most. A good performance over the month will get you quite far...and practically not consider numbers as much.