If your CO is 4.28 %, you're running way too rich.
This could well be the sign of a defective oxygen sensor.
May be worth while replacing it, as you're also waisting a ton of fuel.
I installed an aftermarket catalytic converter on my truck about 8 years ago, and it passes the Ontario Drive-Clean Test, every two years, with flying colors.
Mine is made by " Walker " Exhaust.
Check with any good mufflershop.