Just yesterday I managed to calibrate with my new upgrade kit to 4.1 and with firmware .88. I ended the day excited to go to cut today because on a 9x9 grid it gave me a fitness of 0.99 (the best on my maslow).
Today one of the stepper motors on the Z axis (the one below) didn’t want to work, I swapped the connectors and it worked, so it must be the output. Right now it started working and I hope it doesn’t fail in the middle of the cut. 
First edition of text: The stepper motor has stopped working again 
second edition: it’s working again, i think i’m having problems