If this the vacuum version of the shift control then you might want to start at the vacuum line coming off the valve cover. if you have too high a vacuum or the bleeder on top of the Ip is not bleeding off enough vacuum at full or half throttle then you will have flaring also. I tightened up my modulator (really helped) only to realize that I'm pulling 20 at the vacuum valve and then only dropping off to about 8 at full throttle. it should really be about 0 at full throttle so I have too much vacuum.
You can adjust the range of vacuum I am told also by changing the main connector off the vacuum source to reduce the initial vacuum load thereby shortening the vacuum range (theoretically tightening up the shift range).
if this is not vacuum controlled then I think I just did a lot of typing for nothing and sorry to have butt in...
