I was able to adb and fastboot into the device. And I flashed the ATT CU update with fastboot.
After that the device constantly reboots after reaching the M logo screen,
I can boot into the bootloader, and I can send fastboot commands, but not any adb commands.
I also cannot load any of the options in the bootloader (Recovery, Factory, etc), they simply reboot the phone.
I don't care what version of Android I go to as long as it gives me a working phone. Please help!
Edit: I was able to recover my phone by flashing the 4.4 update. I would like to know where I went wrong, so that I could possibly still do the downgrade>root>upgrade path.