ATT UVerse has its limits because it uses ADSL (copper wire); however, ATT does offer GigaBit service outside its U-Verse branding. What you seem to have run across, is one of those grand-fathered, territorial non-compete agreements that all the cable vendors were demanding from the cities and towns they wanted to service back in the 1970's, 80's and 90's.
You can force your local government to break that lease if your bribe is larger than what ATT is currently paying them and you can show your local government there are better, faster, and more reliable services available for them to use.
Here is the proof that ATT offers Gigabit service in Fort Worth, TX. You, however, may live in a suburb of Fort Worth which means your territory is operating under a different, grandfathered lease!
FYI, I live in Houston, TX, 77058 ZipCode, which is a heck of a lot larger than Fort Worth, and I am currently capped at 50/5 too unless I want to spend way over $100 per month just for Internet and telephone fees. That's because I am an existing ATT customer and only NEW customers get the $50/month offer!
I am still trying to find out who, or which local governmental agency, owns the ATT lease for my townhouse complex which has well over 200 units in it. Comcast (aka ComCrap) has the leases for all the rental apartments across the street but Comcast will not install their Gigabit network in my townhouse because of the non-compete territorial clause ATT holds over the territory where my townhouse is located.
Now, how is that for feudalistic, monopolistic, corporate greed? I hope you get better results than I have gotten to date. Just remember that this is Texas politics doing its worst to fill its representatives' pockets at the expense of yours!