My 6.0 is having an intermittent issue. It runs great, but sometimes it will start to surge bad when I return it to an idle. RPM gauge wont move, but it surges. I had the injectors tested to rule them out they are fine. Has a new EBP sensor. The only thing I've found is a hole rusted in the bottom of my downpipe, could this be an issue that would make this happen? Obviously I'm going to fix it, but just want to start having ideas on where to look. Thanks.