Shift points are determined by the vac modulator on a Turbo 400. It does not have a cable like the Turbo 350. You also need to check the downshift points. That is actuated by an electrical signal or switch hooked to the throttle some how in most cases. Aftermarket Vac modulators will respond to lower amounts or signal if you have a wilder cam.
Remove the hose from the unit and turning screw inside the tube that the hose pushes on is how to adjust. IN is a higher RPM..... give her 2 full turns as a start point.