Have you checked the Hoagies Gifted Education Page,
Psychologists familiar with the gifted? There are a few under 3 hours from Houston (Austin, San Antonio) and a couple more about 4 hours from Houston (Colleyville and Denton... near Dallas).
You might also try contacting your State's local affiliate of the National Association for Gifted Children (NAGC): Texas Association for the Gifted and Talented (
TAGT). I notice the TAGT annual conference is being held next week (June 18-20) in San Antonio.
Some families choose their assessment professional without regard to location and then plan a family vacation trip designed to incorporate the testing.