There are two ways the center shaft bearing can fail. first, the bearings themselves can fail, second, the rubber isolator the bearing is centered in can dry rot and fail to.

My rubber isolator was shot and it caused a wobble at certain speeds which transmitted shake, or vibration.

If you can get one eyeball with a flash light to look down the pan tunnel and move the drive shaft up and down, or side to side, you should be able to see if that rubber isolator is compromised.