my car

Now all you have to do is replace the head gaskets & cats

It's possible you still have air trapped in the system. For some reason these cars are sometimes extremely difficult to get refilled properly. Before ripping the engine apart to change gaskets have a shop drain and refill the system using a vacuum tool that draws all the air out as it is being filled. While you're at it do a compression test which should help determine if the gaskets are OK.