The slightly elevated HC & CO points to a sluggish O2 sensor - the way high NOx is a dead giveaway. At idle, conditions are fairly constant, so the slow acting sensor may still be reacting fast enough to keep the converter in both oxidizing and reducing regions long enough. At higher engine speeds, there's too little time. An analogue voltmenter reading of the O2 sensor output will probably show only 5-6 swings across 0.45V per ten seconds, when it really needs to be higher than 8 times in ten secs.

For NOx failure with low HC & CO, coolant temp would be the place to look.