My auto transmission shifts into 4th gear at 3200 rpm. Seems too high to me. I’ve read 2800 rpm is proper. I’ve adjusted the vacuum regulator which eliminated a downshift clunk coming to a stop and screwed the adjustment screw in until the trans started to slip and then backed off until slip was eliminated. After the shift from 3 to 4 occurs the rpm’s can drop to about 1700 before it up shifts to 4 again. Any ideas how I may be able to get the up shift to occur at a lower rpm?