Are your Z axis rods M8 threaded rod or M8 4 start leadscrews ?
M8 threaded rod at 1.25 pitch should be 2560 steps/mm at 1/16 microstepping. 4 start leadscrews would be 400 steps
M8 threaded rod at 1.25 pitch should be 2560 steps/mm at 1/16 microstepping. 4 start leadscrews would be 400 steps