emission test failed. print out says gross polluter.truck idles and drives good

Try adding some carbon cleaner/fuel treatment to your fuel tank, drive it a 100 miles, change the oil and retest. The carbon build up may be causing the failure.

are we talking 2300 nox if so cleaner is not going to fix it. possible causes egr system not working correctly,o2 sensors not working correctly,catalytic converter not working correctly,very severe carbon build up.could be one of these or a combination.I would recommend you bring it in for diagnoses it will save you money and time in the long run.we are here in Oceanside 760-757-9615