Please confirm that this is a bad headgasket.

[Isphius]

For your high nox, replace your cat and see if your egr is working. I am not 100% sure on this, but my 7mge had a minor hg leak and my nox were 3x higher than passing. I never fixed it and went back to inspection thou so i dont know if that was a cause. And that was with a working egr valve. and old cat. To test the egr, Way at the back of the motor on the driver side there is a round thing bolted to your intake, And the vaccum line that goes to the back of it is your egr valve. Plug that vaccum line into a direct vaccum, Like the one at the very back on the intake. If your motor coughs or sputters, It is working. It may even stall. And im not sure how to test the modulator (round part), But those are very easy to replace if bad. As long as your valve works and coughs the engine out your ok.