So I went back today, after switching out my ecu and putting a stock one and it failed again. Not as bad this time. And it actually passed at 25mph but failed 15mph. Most of the results are really close to the limit however. This time the NO was too high at 15 mph. The guy said that the reason now is my cat. Is that all there could be?

NO (PPM)
15 mph
Max: 708
Meas: 812

Thats the only thing that was over the limit... Plz help me out. Thanx