Okay I have searched for a datasheet to your stepper. It seems it has 200 steps per rotation. So with 1/8 step 1600 in the code is correct.
I realized just yet that the stepper connectors on the shield are odd. From top to bottom it states for x-axis :
X01A
X01B
X02A
X02B
for as on the original easydriver the connectors are :
A
A
B
B
Today I tried it again but got the same jittering and step skipping.
I used GRBL for arduino and adjusted the Port pinout in the source to match the approriate pins on the shield. Still to no avail.
Ill get this china shield to work. Cost what it may.