Update: should have researched a bit more on XDA before looking :P..., so this is more of a info thread now xD
N9005 LTE Bands: 800 / 850 / 900 / 1,800 / 2,100 / 2,600MHz
AT&T's Current LTE Bands: 700 / 1700 / 1900MHz
The best bet for anyone looking for an unlocked bootloader GN3 that works with AT&Ts LTE network is a carrier unlocked T-Mobile variant with a proper radio flashed & APN settings. Otherwise bite the bullet and deal with SafeStrap.