Usually dropping the real lower control arm mounting point by 1 inch or so is sufficient to change the Instant Center enough to be advantageous for helping the car hook.
If more than 1 inch, then you should certainly check your pinion angle.
On average, with stock bushings in the rear upper and
lower control arms, having 1.5-2.0* pinion down angle is needed due to bushing deflection under acceleration.
If you have Urethane bushings then only .75 to 1.0* pinion down angle is required as there is less deflection in the control arm bushings.
With Heim Joints or solid bushings, then near 0* down angle is required as no real deflection is taking place.
Ideally you want the driveshaft at 0* front and rear when under acceleration as this provides the least amount of friction in the drivetrain.
If you have more than 2* of pinion angle, then I suspect that this is the source of your vibration.
Typically, U-joints are designed to work with up to 1.5* of angle each. So 2 U-joints should handle 3* of angle total. This is why double cardan joints are used in some applications to accommodate more severe driveline angles..................................................^^^^
Should is the key word.