I'm a good skier, giant slalom is easy for me, but I want to do better in slalom. My height is 170cm and my skis are 165cm. I've noticed that guys who train in slalom, and are at least 20cm taller than me, use 165cm skis. While this didn't cause trouble for me in giant, in slalom I can hardly move, starting to skid and loose speed!
Should I change skis or should I work more on my slalom hoping it will improve?
It is vey difficult to anser withou knowing your "style" and your weight.
I try to give you general info:
This ski size from Atomic brand shows that ski size for slalom race should be shorter than the racer 
This table says that you can use ski from 150 to 165 according to your hieght, I can suggest you to choose a ski near to 150cm if you are lighter of near to 165 if you are havier
I think ski lenght around 155cm should be the right way
