i have a 2007 3500 cummins, i want to straight pipe it but don't know if i should do the muffler and cat or just muffler. ive heard from about half the people ive talked to not to take off the cat becouse of an o2 sensor back there. ive looked and there isn't any sensor on my exhaust, so am i missing something? can the cat be taken off and not affect the computer and performance in a bad way?