>From your description is sounds like it is a part of the driveline out of balance and that it depends on speed. Additionally you describe symptoms that are getting worse as more time is spent driving. I am not so sure it is a wheel bearing... not to sound like an ass, but are you certain the drive-shaft fasteners are tight (and haven't backed off in torque since the job was completed)? That the drive-shaft is mated to the tranny hub correctly? That the axle nut is tight? Just a thought...
Good luck Jon
