HC and CO indicate that the catalyst is probably okay. If there was any detonation during the test, this could increase NOx, so I recommend premium for the retest, but make sure the engine is hot as was the case with this test. The engine and cat need to be hot to keep HC below the ragged edge.

Since NOx is the only real issue you should thoroughly check the EGR valve control system to be sure it's functioning properly.

Duke