A factory shop manual might give you some clues about which signals you could tweak to fool your transmission but my own research on the subject for my Caravan lead me to believe that in my case such tweaks would also have a negative effect on driveability, emissions, and mileage. You might want to check into a performance valve body for your transmission (if available) to firm up your shifts and maybe offer some manual control. If your manual leads you to think that electronic tweaks are possible try this website for info:
Browser Warning