How do you have it set up? with the pully pushing up or down on the chain? Sometimes if thoes types of tensioners are set up to push the chain down, the chain will not wrap around the cog enough and you'll get the chain to skip.
I had this problem on a customers bike not too long ago. They had the surly tensioner set up so the chain was being pushed down. I reversed it with the other spring it came with so the pully pushed the chain up and the skipping went away.