Look into possibly a defective or contaminated MAF (mass air flow) sensor and/or low fuel pressure faults. More than likely your Infiniti G35 is running lean causing the ECU to increase fuel trim. This condition may cause a false catalytic converter efficiency code and is considered a "fake" breathing problem.
If fuel trim is high at idle AND at 65 mph diagnose further for a vacuum leak behind the throttle plate.
We also recommend ensuring your Infiniti's oxygen sensors are working properly by administering a propane enrichment test. Check that O2 voltage switches below .02 to above .09 when propane is added. Note the rear oxygen sensors should produce a relatively flat .45 volts during steady load.
