I was taking a looking at my stock muffler and noticed a very small crack where the hanger met the muffler. I think I am going to go with the Resonator. It looks like coming off the turbo, it is a 4" pipe that is adapted up to a 5".<br/>I have seen posts where some used 4" and some use 5". I have a 2001 Cummins 8.3.<br/>Any suggestions on sizing? Should I adapt it to a 5"...