I heard that some of the towers previously broadcasting LTE aren't or weren't anymore. I know Galleria Blvd was spotty with LTE when I was around there, so most likely its the network not your phone.
My girl has the HTC One on T-Mobile and she pick up LTE everywhere we go. Even in the middle of the Best Buy off Birdcage in Citrus Heights. I don't get any data at all in any of the Best Buys usually on my phone. Its usually not a phone issue and more of a network issue when data is bad. But it is possible to get bad devices, nothing is perfect.
You can have a tech check out the phone if you actually think its your device though. On that note, the S4 is a better phone spec wise and I like it more personally. But the One is a good device to, just not for me. Did you do the most recent software update? I know it added the feature of HD voice among other things. Sent from my Sprint Galaxy S4 using Tapatalk 2