Marlin - setting up aNema 17 with planetary gearbox reduction (no replies)

Hi guys, I would like to ask for some ideas, because I've exhausted mines abut this.

For the Z axis I was using a stepper motor attached to some guide rails and was managed to get it working fine, but had to upgrade to a new motor with a 1:26.85 reduction gearbox.

The problem is, to any value of steps per mm that i put in from 50 to 2600 (the calculation of the correct value for this setup is 2600) I always get half turn on the shaft. Always the same movement for different step/mm value!

Is there any other setting in Marlin that controls this?

see specs here: link

I'm using Arduino Mega with Ramps 1.4 and Marlin firmware and full steps.

Settings on movement (note not using E movements):

#define DEFAULT_AXIS_STEPS_PER_UNIT { 3 , 3 , 2600 , 500 }
#define DEFAULT_MAX_FEEDRATE { 4000, 4000, 2000, 25 }
#define DEFAULT_MAX_ACCELERATION { 500, 500, 500, 50 }

#define DEFAULT_XJERK 5.0
#define DEFAULT_YJERK 5.0
#define DEFAULT_ZJERK 1.0
#define DEFAULT_EJERK 5.0

Thanks.