I have a 2003 Chevrolet Trailblazer. Mileage 186,000. It has the original engine and transmission 4.2 L Vortec and an automatic 4L60E transmission. I have the code Po440. The code doesn't come on when I start the car, it comes on  when I'm driving. I also get a Po420 once and a while. The car has has a ruff idol when I start it and rev's itself up and down until it settles down after a few minutes. The car also hesitates and bogs down when I go to accelerate at a red light. We have done a full leak down test and the only place that we found that leaks is the gas cap. Could this cause those problems that I'm having?

Thank you

We have already replaced all of these parts.

Trailblazer Parts Replaced List 2023/2025

Air Filter

Vent Valve

Purge Valve

Evap Canister

MAP Sensor

Hose to Purge Valve and both Evap ends replaced to hose

Air Intake Manifold

Air Intake Manifold Seals

Throttle Body Seal

Air Intake Bottom Hose

Brake Servo Intake Seal

Evap Air Temperature Sensor and Pig Tail wire

Fuel Filter

Fuel Pump

Fuel Injectors Replaced 6x 2023 all replaced

Fuel Tank Pressure Sensor Acdelco

Fuel Regulator Pressure Valve

Fuel Regulator Pressure Valve / Rubber Hose Ends Replaced

Fuel Return Line Hose and Hose Ends To Fuel Rail are both Replaced

Battery 2023

Alternator

Alternator Pig Tail Wire

Spark Plugs 6x Replaced 6/20/2023

Ignition Coils Were All Replaced in 2019

Camshaft Solenoid Sensor

Camshaft Position Sensor

Crankshaft Position Sensor 

Both Kock Sensors

All power Steering Lines Replaced and Power Steering Pump Replaced

Power Steering Cooling Unit

Power Steering Cup Seals Replaced

Transmission Lines 3/4 Replaced

Three Transmission solenoids/ First To Second Gear

Exhaust Manifold

Exhaust Manifold Heat Sheild

Exhaust Manifold Metal Gasket

Catalytic Converter Pipe Section

Middle Muffler

End Tail Pipe Piece

Bank 1 and Bank 2 Oxygen Sensors

Fan Clutch

Antifreeze Cap

Coolant Temperature Senor

Engine Thermostat Replaced Drivers Side