CA Smog test

So here's the problem My car is having trouble passing CA smog test. I have taken the car to two different mechanics and they can't figure out why it's not passing the smog test. They both said all emission components are working properly and the last resort was to replace the CAT. The results for the smog test before Replacing the CAT are as follows:
15 mph CO2-12.7, O2-2.9, HC-Max-58 meas-27, CO-max-.48 meas-0, Nox-Max-483 meas-899, Fail;
25 mph CO2-13.6, O2-1.6, HC-Max-34 meas-15, CO-max-.46 meas-.02, NOX- Max-706 meas-225, pass

The results after the CAT replacement are as follows:
15 mph CO2-14.8, O2-0, HC-Max-58 meas-10, CO-Max-.48 meas-0, NOX-max-483 meas-66, pass;
25 mph CO2-14.5, O2-.3, HC-max-34-meas-14, CO-max-.46-meas-0, NOX-max-706-meas-912, fail.

I hope someone can help me.