I recently traded for a 99 ej8 civic ex. It is a little ricey and has some non stock parts. I need some help and trying to learn as much as I can. I am very passionate about cars. My rpm gauge I'm almost positive is not the factory one, it isn't reading right. It says I'm at 4k when my car sounds and feels like it's around 2500 Rpms. My speedometer also does not work. So.. How do I fix this?

Thank you,
Christina