I had my Note 3 AT&T bricked and stuck in bootloop too, from Android 4.4 KitKat OTA upgrade too. The method linked below helped me to unbrick it, but note that it's based on the KitKat version leaked from AT&T in January, and it will not take the official OTA upgrade, nor can you downgrade from it to any lower version. Folks are working on a way to upgrade it to the official OTA, and independent work is done on rooting, I'm sure, but for now I'm stacked with the "leaked KitKat". Nevertheless it works very well, no issues with it whatsoever. Even my biggest complaint against version 4.3 - the GPS issue, is fixed now. Read more about this unbrick method at:
http://xdaforums.com/showthread.php?p=51572014#post51572014
Greg