My friend has a 2004.5 Cummins 600 with a 6" exhaust and the Power Pup. The truck ran fine for a while but then the SES light came on and it started running rough. He took it to the dealer after he removed the Pup's program and they old him his ECM was bad and he needed a new one. They also asked him if he had a programer on the truck. Apparently the truck will throw a specific code that tells the dealer he had a programer installed. Have any of you guys had this problem, and do you know of a solution? He doesn't want to blow another ECM by installing the Pup again. They replaced the ECM under warranty, and all is well.