2000 Pontiac Bonneville 2000 Bonneville Vibration at 46-54

Drive Train Axles Bearings problem
2000 Pontiac Bonneville 6 cyl Front Wheel Drive Automatic

My 2000 Bonneville has a vibration only when accelerating and only between 46 & 54 mph. I have had the tires rotated and balanced 3 times. I have replaced the brakes rotors calipers. I replaced a worn tie rod end. I had a front end inspection done. I replaced both front hub assemblies. Any idea what could cause this. It shakes the whole car when accelerating lightly and if you let off the gas it stops instantly.