RegionLockAway by Chainfire seems to remove the network lock on this specific model, despite being designed for the Galaxy Note 3.
(original thread) http://forum.xda-developers.com/show....php?t=2470551
Now, I've tried this on my phone, and as I said before, it seems to have removed the network lock on my SGH-T999L, but only partially. I am no longer bothered for an unlock code when booting the phone with an AT&T or MetroPCS SIM card inserted, and my account details assigned to the SIM cards are displayed under my phone's settings. The issue is that I cannot seem to connect to any networks.
I don't know if this will lead to anything, but I just felt like sharing this little tidbit of information with you guys. If anyone else would like to try this out and post results, I'm sure it would be greatly appreciated by the community. Hopefully this gets us one step closer to unlocking this bastard of a phone with minimal effort.
P.S. If this is in the wrong section, feel free to move it, and I apologize.