I think this is more about how AT&T manages their network internally, than an issue with the Titan.
When I run Bandwidth to test speed, it picks Seattle as the server because that's geographically nearest to me. In one particular location on the ground floor in my house I get anywhere from 0.5 to ~1.5Mbit. Upstairs I can get 2.5-3.5Mbit.
However, whatismyipaddress.com geolocates me in Sacramento. When I do a speed test to Auburn, CA, I get 3.5-4Mbit downstairs and 5-6Mbit upstairs.
Now... 5-6Mbit ain't setting the world on fire, but at least I know my phone isn't broken, and the device isn't artificially limited to some piss-poor speed. On a class 10 device, 5-6Mbit isn't too bad.