High NOx is formed by high combustion temperatures. Usually this is either a lean mixture or misfire/preignition. If your CCV leak was big enough that the PCM couldn't adjust the fuel to compensate it could go lean enough to spike the NOx. It would probably throw a check engine light though. Easy enough to fix the leak and have the test rerun.
If you have worn ignition components that can also contribute to NOx.
Your cat should be scrubbing the NOx though. Make sure to get your Jeep good and hot by driving it for awhile preferably on the highway not stop and start driving for a good ten or fifteen minutes before taking back to get checked. Your cat doesn't work unless it's hot. This especially true if you picked an aftermarket cat that may be more universal, high flow, performance oriented.