Try setting nos off at 2-300 rpms below shift rpms. Example = SHIFT RPMS 11.000, NOS OFF 10.800 RPMS. Unloads motor just enough to help the 4-5th or 5-6th shift issues. Wont help if trans is not right or going away,but if its just a big shot issue that you can't quite work out with kill time or shift delay,then give this a try....