there was a few more mods made to mid range D6Cs than just bolting a turbo on when they changed from a NA D333C to the turbocharged D333C. We had a lot of early NA 69J D6Cs here and a lot of people thought the earlier 76As went better. Best you can do with your one is check the converter stall speed and go from there, with regard to checking injectors, valve lash, rack setting. Take it you have changed the air and fuel filters first ????