0.5mm Thin wall printing issue

I build my 1st prusa a couple of month ago but had to rebuilt recently.

I'm having an issue that my 0.5mm thin wall is having problems nearer to the top of the print.
I've attached a photo showing my orginal 0.5mm thin wall on the left which I was happy with alongside my current thin wall on the right. As you can see my current print is much lower than the orginal and the layers near the top look squased all of sudden.
Anyone know why these layers near the top is all squased on then resolve themselves for the last few layers?
Also why is the cube so much lower than the original? Z-axis has been calibrated and moves 40mm when I instruct 40mm.
And lastly the place where the the z-axis steps to the next level is now in the middle of the side creating a grove, where it used to be on the corner. Any idea what is causing this?

My current nozzle is 0.35mm and my layer hight is set to 0.28mm.

Any help would be appreciated.

im using repetier and used to have the same problems with my z motors. the motors were cheap so i switched them with high torque kysan nema 17s, i also changed the current control in repetier config from 135 to 170 because that current drives 2 z motors. keep an eye on heat when upping current though

hi,

the stepper motors I'm using is Nema 17 model Model 17HS19-1684S that I bought from Think3dprint3d.
Holding torque is 44 N.cm (4.4kg.cm, 62oz.in). they seemed ok according to the reviews. do you think need to replace?
1 more thing though. the lefthand print was done when the motors were at the top of the machine but in the rebuilt I've mounted them at the bottom. Will this make a difference?
I'll try to play around with the current tonight and see what happens. What would be a "normal"/acceptable temp on my pololu board with the higher current?

This has been resolved now.

In case anyone else have this problem...

I couldn't get to changing my current because I couldn't find the settings In Malin, so I first increased the voltage on my pololu board which resulted in higher temparture on the board and my print worsening.
then tried lowering the voltage on the board and the print came out perfect.
Also the grove you can see on the side of the wall disappeared when I changed my layer hight from 0.28mm to 0.2mm.

Hope this helps someone.

check your attachment between Z threaded rod and motors, mark the threaded rod, connector and motor shaft and try again, marks should remain lined up through the process, a little slip on hard acceleration may be the cause

This can also be caused by backlash on the z axis ... make sure the springs on the carriage nuts move freely and liberally oiled