Since this is the first thing that comes up on Google when searching for Galaxy S4 AT&T 4.4.2 root, I'm going to post in here. I'm rooted! Here's how:
1. Go to www.towelroot.com
and grab version 1. Install it.
2. Go into your Application Manager, flip to the right, find Lookout, disable it.
3. Run Towelroot. It won't tell you much, probably crash, then reboot.
4. When you boot back up you should have totally unrestricted root access. Check it with Root Checker.
5. Install SuperSU from the Play Store, let it update SU and disable Knox.
6. Enjoy your rooted, stock 4.4.2 TouchWiz ROM!
I verified root with Root Checker, Adfree Android, and Titanium Backup. All appear to be working.
Samsung Galaxy S III SGH-I747
[Rom] Slim 4.3.1 Build 2
[Recovery] TWRP 22.214.171.124