I should point out that from my wrx days, one would never increase flow without corresponding work on the fuel map. Granted, on a turbo the consequences of going lean can be worse, but I think it would be hard to say the 261 is at fault. My nox spiking seems to happen in the 3k + range. I think if I truly am lean that could be attributed to the higher flow from the head and exhaust.

I should also point out that my previous truck, with the 252 and open exhaust, just barely passed emissions with 5.7/6 allowed. I don't know if those numbers are truly high, or if that is some arbitrary number set by Colorado.