Look at your logbooks. Was the wastegate or controller recently changed and how much time is on your turbocharger. The wastegate butterfly could be sticking due to carbon buildup or TIS (time in service) Check the lines to both the controller and wastegate for leaks. If your controller was recently changed out, the settings might need to be adjusted. Lots of times they are overly field adjusted. Mark where you start and move in small increments.