High NOX is often associated with EGR valve malfunction. You can do a quick check of your EGR by locating the EGR valve and holding your finger on the bottom of it as you rev the engine by moving the throttle under the hood. (Take off your tie before you try this!)
If the plate on the underside of the EGR moves up as you rev, the valve is probably working OK. If not, then you may have an issue here. The most common cause is a blockage in the metal tube that operates the EGR through the BPT valve. This tube is connected to the BPT via a rubber hose and delivers a vacuum signal from the larger pipe that goes from the exhaust manifold to the intake manifold.
If none of this is making sense to you, do some searching on this and the other forum. There are many pictures and detailed explanations. Your car won't pass NOX if the EGR is not working.
Our cars are getting so old that many shops don't even know how to work on the emissions systems any more. We have to fend for ourselves.