So I have a P1133 ‘HO2S Insufficient Switching Sensor 1’ code and P0300 misfire code but I’ve replaced the following items: ACDELCO O2 sensor bank 1 sensor 1, MAP Sensor, camshaft sensor, new spark plugs and spark plug wires and fuel injectors, also did a smoke test for vacuum and exhaust leaks (none leaks) and the P1133 and misfire codes just keep coming back after drive cycle completes.. current tuner says he deleted those O2 sensor codes from my tune file as I have LT Headers.. it continues to not run great mostly when cold and it also smells of gas through the exhaust. It’s at my mechanic shop right now and even he is at a loss and also racking up a large bill trying to solve it and pass inspection…

Things I havent checked: battery, fuel pump, fuel lines.

Anyone experienced this before? appreciate any advice you have...

Motor was built March 2021 from previous owner and I am in contact with his mechanic who built the motor which is helpful.

Mods list:
Gpi ss2 vvt cam
Longtube headers
Br pushrods
Btr trunion kit
Ls7 lifters
Afm/dod delete
New timing chain and tensioner
New plugs
Spark plug wire covers
X pipe & spintech 9000 mufflers
Cold air intake
Moroso oil catch can