vibration at 2000 rpm

96 xj auto with 99 motor. I bought this vehicle with a blown motor, replaced with 99xj motor with 110k miles. when torque converter is bolted up and engine is revved up there is a noisy vibration starts around 1700 and goes away around 2300rpm. I have tried rotating the flex-plate to stop the vibration and it will quiet down but not go away no matter which way it is bolted up. Also flex-plate did not come with engine was bought at salvage yard and matched up to original w/ wallowed out torque converter holes.
Any help would be appreciated.

Did you check closely for cracks in the replacement flexplate?

Is the trans original to the 96 with the wallowed out flexplate mounting holes? Maybe some damage was done to the torque converter/front pump of the trans running with the flexplate loose.