chain jumping when puilling away in a higher gear
When you replace the cluster (rear cogs) you almost always need to replace the chain too because they wear together.  If you put an old chain on a new cluster, you often experience that kind of because the length* of the links in the chain is slightly longer than the spaces between the teeth on a new cluster.

*Note the links don't actually get longer, it's just that the rollers wear out and allow a little play and the links sit a little further apart.  This is known as "stretch" though it's different to the way something like elastic stretches.