The trans upshifts are controlled by governor pressure over coming throttle pressure. If the kick down is adjusted as far back as you can go,then you will have to modify the governor. A&A sells them and they can be changed in the car. If your cheap like me you can modify your own. Drilling the inner weight with a 3/8" bit 3/8" deep. Take the outer weight reduce the diameter by 1/8". Leave .100" untouched on both ends so it still fits correctly in the bore. This will get you pretty close.
Doug