The lte apn should already by set it should be called AT&T PTA if not just hit menu button and reset to default
The 4g/3g apn info is below
I have 2 separate apn the AT&T has a special apn for late which is pta. But I also have the 3G/4G apn
This are the setting just go it to setting, more settings (under wireless and network), access point names(apn), and click menu to make a new apn and fill in the fields with the information below (make sure u make what is caps be caps or it will not work)
Name: AT&T
APN: wap.cingular
Proxy: leave blank
Port: leave blank
Username:WAP@CINGULARGPRS.COM
Password:CINGULAR1 (yes this is in CAPS)
Server: leave blank
MMSC:*
http://mmsc.cingular.com
MMS Proxy: wireless.cingular.com
MMS Port: 80
MCC:310
MNC:410APN Type: leave blank
Lte chips do use more battery and since lte is everywhere where 4g/3g they work more to get the signal and end up killing more battery.