problem

If you are still looking for answers regarding the delayed shift problem with your 1997 Pontiac Trans Sport van there are two items you can easily inspect. One is the vacuum modulator which you previously said has been replaced and the vacuum source completely inspected and functioning correctly. And the other would be the TV cable if equipped. Generally speaking the TV cable is for kick-down and the vacuum modulator controls the upshifts. Incorrect engine data to the powertrain control module (PCM) may also cause incorrect transmission shifts. You will need a scan tool to monitor the PCM date to see if any sensors are out of range. If you do not have access to a scan tool perhaps it is time to take your van to a qualified transmission shop for diagnostic inspection.