z3V root and flash problem

So, here I'm stuck with the z3v after my 6plus sold to my uncle. Running E.44 and the root method seem not working, I already install the king root and can't replace with the superSu, keep saying "fail to update, reboot"... and trying to degrade firmware and the flash tool keep said "can't reconize device, check the driver....." Saw topic with instruction to kkng root temperary and "dual recovery" what's the dual recovery is it?
Is it possible that verizon will open bootloader for z3v??