NO should actually be "NOx" - for "oxides of nitrogen." They contribute to acid rain.
NOx is typically caused by elevated combustion temperatures, and is solved either by the EGR (which system is of dubious utility below 9.0:1CR...) or by the first catalyst bed (the modern three-stage catalytic converter does three things; 1) reduce NOx to N2 and O2, 2) Oxidise CO into CO2, 3) Oxidise HC into H2O and CO2. The oxygen liberated in the initial reduction reaction drives the second two oxidation reactions.)
If your cat is original, it could be on its way out. Between the alleged "poisoning" of the catalyst bed by organometallic additives (used for scuff protection) in oils rated API SL or earlier, and coating with exhaust carbon over time, they do eventually stop working. Since your 1995 doesn't have the EGR system, you might want to start with running Seafoam (or some other cleaner) down the intake to clean carbon deposits from the combustion chambers, then replacing the catalytic converter about a month later (since yours is already likely to be just about shot, blow the carbon out first. That way, you don't get carbon deposits all over your nice new catalyst matrix...)
