2G/GSM Only. Not 3G/4G LTE

I received my HTC One M8, (I'm from Chile) and put the ENTEL PCS Nano-SIM, and no signal and sometimes takes the 2G network only, and then falls again. Never takes 3G / 4G signal. I've never changed ROM, comes with the original ROM. My HTC One M8 is AT&T version, with Android 6.0.

This is my bootloader version.

Code:

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» fastboot  getvar all
(bootloader) version: 0.5
(bootloader) version-bootloader: 3.19.0.0000
(bootloader) version-baseband: 1.29.214500021.12G
(bootloader) version-cpld: None
(bootloader) version-microp: None
(bootloader) version-main: 6.12.401.4
(bootloader) version-misc: PVT SHIP S-ON
(bootloader) serialno: FA43MWM05338
(bootloader) imei: Deleted by me
(bootloader) imei2: Not Support
(bootloader) meid: 00000000000000
(bootloader) product: m8_ul_ca
(bootloader) platform: hTCBmsm8974
(bootloader) modelid: 0P6B10000
(bootloader) cidnum: 11111111
(bootloader) battery-status: good
(bootloader) battery-voltage: 0mV
(bootloader) partition-layout: Generic
(bootloader) security: on
(bootloader) build-mode: SHIP
(bootloader) boot-mode: FASTBOOT
(bootloader) commitno-bootloader: 76df2b54
(bootloader) hbootpreupdate: 11
(bootloader) gencheckpt: 0
all: Done!
finished. total time: 0.046s

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