[Moto X General] rczrider:
This worked for me on the XT1058 (AT&T variant) with version LPA23.12-21.7. Thanks to [MENTION=6305524]drrobo[/MENTION] for the heads up about doing the flash manually, as RSD Lite didn't work for me, either. And since some people (myself included) like really detailed instructions to make sure they're not forgetting something or messing it up, here is what I did:

Install Motorola drivers (Motorola Device Manager): https://motorola-global-portal.custhelp.com/app/answers/prod_detail/a_id/94931/p/30,6720,8696\

Install Python 2.7.9 (32-bit, even though I have 64-bit system): https://www.python.org/downloads/release/python-279/

Install Serial Port Extension 2.7: http://sourceforge.net/projects/pyserial/files/pyserial/2.7/pyserial-2.7.win32.exe/download

Install Minimal ADB and Fastboot (to C:\MinimalADB): http://xdaforums.com/showthread.php?t=2317790

Download and extract mfastboot into ADB directory: http://xdaforums.com/attachment.php?attachmentid=2427667&d=1385958280

Download and extract zip file contents into ADB directory (ATT_XT1058_5.1.0_LPA23.12-21.7_cid1_CFC.xml.zip): https://yadi.sk/d/MCliEyCPfj7ZZ/MOTO.X1/XT1058/ATT

Download tools and extract to C:\Python27: https://yadi.sk/d/WDUlvQgtiQNbv/MotoX/LPA23.12-21.7

Download QDLoad9008 Drivers and unzip own directory (DRV_QHSUSB_QDLoad9008.zip): https://yadi.sk/d/p458Cy0XineRC/QDLoad9008 Drivers

Install QDLoad9008 drivers (I used DRV_QHSUSB_QDLoad9008\WinXP_Win7_Win8_Win10\x64\DRV_INSTALL_x64.exe)

In phone, enable Developer Options (Settings > About phone > tap "Build number" until it says you're a developer)

In phone, turn on USB Debugging (Settings > Developer options > toggle "USB debugging")

Plug phone into computer and check "Always allow from this computer" when "Allow USB debugging?" box pops up

Run ADB via command line and type "adb devices" to ensure phone shows up

Type "adb reboot bootloader" to put the phone in fastboot mode

Wait for computer to recognize phone and install drivers

Use the following commands (and note the line with mfastboot instead of fastboot...that is intentional!)

fastboot oem fb_mode_set
fastboot flash partition gpt.bin
fastboot flash motoboot motoboot.img
fastboot flash logo logo.bin
fastboot flash boot boot.img
fastboot flash recovery recovery.img
mfastboot flash system system.img -P
fastboot flash modem NON-HLOS.bin
fastboot erase modemst1
fastboot erase modemst2
fastboot flash fsg fsg.mbn
fastboot erase cache
fastboot erase userdata
fastboot erase customize
fastboot erase clogo
fastboot oem config carrier att
fastboot oem fb_mode_clear
exit

Run BLBROKE.bat

Verify that QDLoad9008 drivers are correctly installed *

Run RUN_Root.bat **

* Windows said my drivers were installed, but RUN_Root failed. I went to Device Manager > Ports and uninstalled, deleting the drivers as well. I unplugged the phone and then back in and then watched the window about installing drivers. It was downloading drivers from Windows Update, so I cancelled that. It then used the "correct" drivers from the OP that I had already installed.

** This took a while, maybe 10 minutes? And then the phone sat on the boot logo for another couple of minutes before booting up. Be patient.