If your car is upshifting at too high a speed, but shift harshness is OK, LENGTHEN the bowden cable going to the tranny a little. The Vacuum modulator on the tranny works inversely--the more engine load (lower vacuum) the higher the shifting pressure (firmer shifts) and the higher the speed at which the tranny will upshift. Adjust the Bowden Cable to change the light throttle shifting speeds. LENGTHEN if to LOWER the shift speed.

Adjust the vacuum modulator to regulate the line pressure (which controls shifting firmness) ONLY if you know what you are doing--you can cuse problems by messing up the line pressure adjustment with the vacuum modulator adjustment.