Alright i just got the game for PS3 and it game with two dlc so my question is should i download them now or wait till i finish to play them. If it helps story wise im on the third traffic case and i noticed that one of the dlcs is a traffic case so should i download that one and play since thats where im at or just wait till im completely done?

I'd say go ahead and download them. They are completely fine on their own but they might add some enjoyment to the story for you personally.

Yes, download them before you play. That way they're perfectly integrated into the story and you never realize you're playing a DLC mission.

If you've already done a case via the Case menu, and you get to the point in the story where it would fit, the game stops and asks you if you want to skip it. I can't remember if the Slip of the Tongue case is after the second or third traffic mission. If you end up getting promoted before you do the case, you'll have to go and access it through the case menu.

Download it because the game will integrate the case into your play-through.