I got a DPF/SCR race pipe. Just looked under the truck and two large area's in the exhaust. one up front and one in the rear. I'm assuming one is DPF and the other a cat. Does the DPF/SCR remove both or just the DPF? If it does remove just the DPF is the DPF the front larger item and the cat in the rear? I'm assuming so based on looking.