are you getting an SES light? even if not, check your mass air flow sensor. i replaced the front O2 sensor and the MAF when i got the car, i don't know how it was even running. did you change both O2 sensors? if it idles smooth and it's just a dog when you're driving, you could have some flow problems. check your filters, oil, plugs and plug wires, little stuff like that. do you have a gt or a gtp? how many miles?also, i bought my mom a new car to get her grand prix from her, and there was a bird's nest in the air filter box lol. you never know what you can find.