[Allbert]

Wild guess is it could be the pressure control solenoid (PCS) causing erratic line pressure and possible slipping / shuddering during and after shifts. My 02 Saturn L would shudder hard on 2-1 downshifts and buck lightly on 2-3 / 3-4 upshifts until I swapped the PCS. If the vibration goes away when you shift into neutral though, then this would not be the issue.