Check if your truck has a cat on it. mine didnt have one stock lol, so i didnt put one on aftermarket. Im in az, and i havent read anything about exhaust noise..especially with a diesel. just to be safe, put a muff on but get a flow through. no restriction
If your worried about the cat, get one and hollow it out. at emmisions they just make you spool the turbo a few times and make sure you dont coal TOO much.
BTW im in Arizona so laws might be different.