Well I have a couple question for you before I will be able to determine the cause of your civic not working properly.
1.) Do you have any stickers on the car?
2.) Do you have a big spoiler on the back to provide downforce to the none driving wheels?
3.) Do you have a ground effects kits that is a different color than the rest of the car?
4.) When you replaced the cat converter did you also add a big rice can to your exahust system to make it sound really cool?
5.) Did you put a really cool sound system into your car for the extra performance and handling that is required to get up to highway speeds?
Until you answer these questions i will give you my answer based on wht you have told me. It is probably becasue you drive a honda.