did you talk to the dealership about having the rail cleaned? They have a cleaning process that connects to the fuel rail and runs the motor on cleaner alone, no fuel. This concentrates the cleaner through the injectors and rail. Also they should remove the tb and tear it down and clean it all. Also they put you basic injector cleaner inthe tank as well. I'm not sure what it costs but I have seen good results in the past. Just ask for a complete fuel system service but make sure they do it like I said because some of the guys cheapass the process to make time on the job.