Ford Mustang V6 3.7L Convertible 2015 Model

Mileage: 97k

Bought this car two months ago. Car was having a lot of vibrations at different speeds.

Car full body wobbles exactly at same speed irrespective of engine rpm or gear. 

Started with fixing:

1. Changed all four tires new kumho ecsta ps71 235-50R18

2. Changed front suspension (control arms, link rods, tie rods, stablizer, front struts assemebly)

3. Did wheel balancing and alignment  

4. Changed front wheel bearing ( found the front right bearing installed before was third party not even ford genuine)

5. Installed a used driveshaft (checked for any u joints and bends) all good  

Now still vibration is felt exactly between 58-60 km/hr and some times between 88-92km/hr  

if there is more weight in the car and the soft convertible top is open, which most of the weight is shifted towards the back, the car gets stable and vibration are rarely felt  

I know my rear suspension needs repair, but vibration at this specific speed irrespective of Acceleration, Deceleration, Neutral is not something related to suspension  

Also humming sound is heard above 75km/hr which indicates a rear wheel bearing issue. And diminishes around 110km/hr.

passenger seat is continuously shaking and if i keep my hand over it it will shake my hand. Rear view mirror shakes as well depending upon speed range (60 km/hr high vibration, other speeds minor)

High tire pressure(35-36 psi due to hot roads) makes vibration harsher. 

Now two things are possible, checked rear for wheel bearings but with tire mounted doesn’t show much sign of bad wheel bearings. 

either it is wheel bearing or torque converter (but why would it shake in neutral at that speed if related to torque converter)

please advise. Or should I purchase the NVH app and try that out before changing the wheel bearing for rear