What you are getting is unlikely because of missed steps. They would need to be missed in one direction and later in the opposite direction just to compensate.
Missed steps on one motor result in wrong z-position of the corresponding carriage on the tower. You get exactly the same thing when you do not have correctly adjusted end-stop on the tower. The bed z-error because of that looks like this:
[attachment 33903 err.png]
Missed steps on one motor result in wrong z-position of the corresponding carriage on the tower. You get exactly the same thing when you do not have correctly adjusted end-stop on the tower. The bed z-error because of that looks like this:
[attachment 33903 err.png]