2000 Pontiac Grand Am Engine stalls when accelerating from

Hello. Just wanted to say thank you ahead of time for helping me in any way to solve this headach. My 2000 Grand Am SE 3400 3.4L is stalling if too much gas if given while accelerating from a stop. I have checked what vaccum lines I can see. I have also cleaned the MAF, EGR, IAC and Throttle Body flange. None of what I have done has solved the issue. I also installed new plugs and wires. I have heard it could be the MAP sensor, throttle position sensor, ect. Dont have the slightest as to what causes this issue when pushing gas peddle in 3/4 abruptly from dead stop. When it happens: RPMS will drop, lights will dim, car will stall. I can start it again right after, but wish to not have to do this. SES light is on. Codes are: P0306 and code for catalyst efficiency below threshold (Catalatic Converter is removed with straight pipe in its place). Very sorry for such a long post. Please help me with this as I dont have any help where I am and it is my fiance's car and want her to be safe. Thank you very much