Transmission jerking when shifting on 1997 Oldsmobile Regency

Transmission shifts funny from 35-55 if under a slight load. Shifts fine if not under a load and seems to shift ok too if I'm rapidly gaining speed opposed to gradual speed gain.It would jump back and forth when trying to upshift, if I tried to gain speed it evenually shifts up ok and runs fine. Gotten more pronounced the past week or so. It is fine at slower speeds even climbing a steep street. I'm really hoping this is not serious. I put 1/2 qt of fluid in it because it was low but did not help. Could it be a modulator? No engine light on or other lights. Seems not to happens so much when it's cold.

Asked by for the 1997 Oldsmobile Regency
First thing is to put something in the line ( pencil ) and plug it to see if the trans shifting problem is because of the vacuum leak. Then try to find a diagram of the vacuum lines, maybe
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