833 OD vibration

I didn't think about 3rd being direct, that's a good point. I have ran the car on stands in 3rd and the vibration moves to approx. 3500rpm. which still comes out to be about 75mph. If it is the driveshaft, I'm not sure what it could be. I've tried balance and angle changes. Ive checked the run out. when i changed the balance or angles, it gave me a different vibration at a lower rpm in addition to the 75mph vibration. i do have an engine vibration in neutral, but it goes away around 1500rpm. I cant see the engine vibration being directly related to wheel and driveshaft speed.