some friends of mine think I should put on a 4" exaust from the turbo back with a 5" tip, sounds really good but how will it effect my truck? I don't want to hurt my mileage, this will be the only thing I would change as far as what the truck came with stock. I would be removing the cat, but putting a muffler back on, I really don't want the truck to be loud inside the cab. I could also go with duals out the side behind the rear wheels. any help?