1. Place the T-Mobile_4.4.4(NK2)_Stock_Rooted_ROM onto your ext-sdcard.
2. From Safestrap recovery press "Backup" and backup your User Data.
3. Once complete, from the main menu press "Wipe" then "Advanced Wipe" and wipe everything but your ext-sdcard.
4. From the main menu press "Install," then select and install the I337UCUFNJ4_100%_Stock_Rooted_ROM.
5. Once complete, press "Restore" and restore your User Data.
6. From the main menu press "Reboot," then "System." Done!
After following the above process your phone will pause on the T-Mobile splash screen for about 2 minutes before rebooting.
1. The above process will not affect your User Data or Knox Warranty Flag.
2. This process will update your modem, non-hlos, stock recovery, and bootloader to NJ4(4.4.4) which are required for the T-Mobile ROM(NK2) to run correctly on the I337.
3. If you do not already have root access you must first flash the I337UCUFNB1_Rootable_Full_Odin.tar using Odin's PDA slot (AP in Odin v3.09+), root using Towelroot, install Safestrap, then proceed with the above instructions.
benwaffle - for his flashboot script allowing Safestrap to flash the kernel(built into the ROM).