I like to shift my motors, all race motors that I have driven, when they quit pulling hard, not predetermine by someone else work scope up
If you can take the car to a decent drag strip you can test different shift points (500 RPM increments to start with) to see what makes your car the best in the 330 and 1/8 mile times work scope

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)