It has been a while since I have messed with this, but if I am not mistaken, the shift kit will increase the internal pressure, then, as you depress the throttle, the pressure increase as pedal increases via the kickdown linkage (delaying the shift).

I cannot find a link to the kickdown linkage adjustment procedure, however, I always struggled to find a happy medium between good WOT shifts and not shifting too early at part throttle with a shift kit.