Vibration in drivetrain

Alright so I have had this driveline vibration for a while now just wondering all the possibilities. Let me give you some info. It starts around 45mph and goes on from there. It was real bad when I had my drive shaft made. So I had it looked at 4 different times by 4 different shops and they said they got it to balance out perfect. It calmed the vibration down but it's still there. I've put shines in the rear ranging from none to 6 degrees and never made I difference. The motor and torque convertor are brand new this year. There was still a vibration last year with the old motor and torque convertor. Trans was rebuilt last year and so was rear end. So that's pretty much it just hit me up with suggestions I'm open to all. :D