you need to get a DP/Powerlog or headers, you need a custom tuned PCM(not a zzp pcm) preferably from 3800performance.com(they have the DHP PCM which are rated the most safe off the shelf tune by the people on this site) and you could definitely use an air intake of some sorts. The cat back is a waste of money performance wise until you are making 350 WHP.... the exhaust is the most restrictive in the U bend and then the front manifold after that. The stock cat back is fine, performance wise. you should have read the "safely modding your 3800" thread in the general tech section first. Please read it now if you have not done so.....Good luck