unlocking samsung N910t after updating to 5.1.1 or 6.0.1 is not easy because most of time after unlocking successful it still request for code. Meaning After saying unlock successful it does not actually unlock due to the modem has been patched which prevent the unlocking.
How to unlock
1.Download modem N910T FOR UNLOCK-g
2. extract and flash (password: if required www.gem-flash.com)
3.unlock with z3x, Octopus or chimeratools
enjoy unlocking without rooting