I just told you.:D
You can adjust the throttle pressure all you want and it's still going to do that, just at different throttle openings and different road speeds.
It's not a manual trans, so if you want it to stay in second without upshifting then you have to keep it manual second until you want third.
Or maybe get a full manual valve body, as those will be in the gear you have selected at any speed or RPM until you manually change it yourself.
