I used to work for t-mobile and that's the LTE APN...
check on their website the LTE coverage areas around you.
Make a backup of your device and attempt a factory reset.
there were some devices I worked with that the factory reset worked like a magic trick.
Sent from my HTC One using xda app-developers app
: HTC One M7 AT&T (Unlocked, Rooted, Bootloader Unlocked, S-OFF)
: Android Revolution HD 62.0 by Mike1986
Sense 5 Toolbox, Gravity Box [KK],
TWRP v. 188.8.131.52
- Galaxy S4 I337 AT&T unlocked
- Nokia Lumia 920 Unlocked - Dev AT&T ROM