The best and most cost-effective approach is to pull your old cats and pipes and replace the front cat (if you have two, which I think you do) only, because that is almost always the one that goes bad. Replace it with an aftermarket cat of exactly the same type as the original. Don't buy an aftermarket cat and pipe assembly (especially if you have double pipes through the cats) because often they reduce down to one pipe in spots, while the factory pipes stay double all the way. If your front cat has a big section blown out of it, you'll know that's the problem.