Take a look here:
e class="onebox discoursetopic" data-onebox-src="https://forum.whadda.com/t/k8203-upgrade-and-driver-voltage/12845/5">

K8203 upgrade and driver voltage
K8200 3D Printer
K8200 - Wiring and electronics
All, A few weeks ago I decided to upgrade my belt driven extruder (upgraded with an E3D hot-end) by the direct drive extruder as offered in the Velleman K8203 kit. I did not install the included hot-end but modified the angular mount to fit the...
It seems like the new driver board that is supplied with the upgrade can not handle the power needed, which makes the motor skip steps.
Try the solution provided in the thread(Putting the old driver back) and see if that solves the problem somewhat.
I haven’t read through this thread, but it also mentions this upgrade: