360 engine vibration at ~3000rpm

You said that there's no vibration in park, or neutral. That says the vibration is in the driveline. Drive the car, and pay attention to how the vibration feels. Then rotate it 180 degrees, and drive it again. Did the vibration change? Doesn't matter if it's better or worse. If there's any change, it's the driveshaft. If no changes, it's in the pinion angle, rear, etc.