Both of their performance is fine, just Jeff's luck is horrible this year. Did you see that graphic during the race? Every single race has had some type of problem, the smallest thing was a pit road fail, the rest were engines, random crashes (which he was victim), tires, etc.
Kahne had that same bad luck at the start, but is starting to get the results that he deserves, as he has ran up front every race just had random issues that are 95% of the time not his fault.