if u get on it and just before it changes gear(into 2) you feel it the most,,yet when you put the car on a lift you can;t find a thing wrong, this is of course after you changed the mounts, right. I think u have a drive shaft problem,,, not just the center bearing,,Yes it could be that but it could also be the universal joint, you can shake it all you want ,,it want show anything wrong,, remove the drive shaft ,,make sure the center bearing rubber is not torn,make sure the bearing housing is round,,,not round like an egg. then push ,pull,twist, the universal joint ,,,then have some one else check it .. fix that, and u are back on the road. jim