2004 auto g35 coupe 180k miles. I want to make this car run as best as it can, and improve its performance to as good as it’ll allow before forced induction. So far have heard plenum spacer, cold intake, high flow cats, headers & exhaust. Is there anything else I can or should do to make increase the amount the power/ torque in this car

 

Add new spark plugs and an Uprev tune and you're good to go