I have mine inspected by the dealer and they haven't said squat about my straight pipe. From what I understand you do need to keep the kitty on though. Just be wary who you take it to. Once you get here let us know and we'll point you in the right direction.
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Jared
06 Cummins 2500, 2" lift, 35" Cepek Mud Country on OEM wheels, muffler MIA, 5" tip, triple A pillar with trans temp/egt/60 pyro. Diablo Predator