I'm at 91% using KingRoot after applying metrpcs's update. Fingers crossed.
Edit: looks like I may be stuck at 91% then fail 3 times now.
Look, other than the zte zmax pro I also have a zte zmax, the first one and I remember that for that phone you had to turn off the task manager, and then basically make the phone create a buffer overflow when the phone runs out of memory because of the task manager being force stopped and the user overloading the phone wirh high memory apps like a PSP emulator or benchmark app. That would give temp root with king root, next you would type some commands and install twrp and then replace King user with SuperSU to get permanent root. Does anyone think this may be a common theme with these zte phones?