First to your questions. The egr and the flame trap are not the same. The flame trap might be considered to be a pcv. The egr recirculates exhaust gasses to cut down on the oxygen available for combustion. You may have a bad cat, but first you should consider the thing that is the most basic cause of high NOx. This would be excess oxygen or a lean fuel condition. Look for vaccuum leaks. You can spend serious money on hardware when your whole problem is a broken rubber hose or a deteriorated o ring. Check the hoses and the injector seals. I burn lots of fossil fuel for a living, and in order to do so within a very restrictive air license, I have had to learn a lot about combustion. Some of the more coherently expressed ideas were posted in Opinions a month or so back.