Any smog experts out there?

This is what is puzzling to me. It's only the 25MPH Nox reading that is off. The 15MPH Nox reading is fine. The only difference running-wise is the RPM change of a little under 1000RPM, unless there is some component I'm not aware of that takes MPH into consideration and/or the computer does something weird at that speed. I was hoping there was something obvious that I've overlooked and that someone has run into that situation before who knows what it is.