Driveshaft contacting body under braking

My car is a police interceptor and I am getting a noise like the u-joint section of my driveshaft is hitting the under body right between the front seats under heavy braking when it is just me in it or light braking or heavy deceleration if fully loaded with adults. The sound is loud and hard and can be felt through the seat. On inspection underneath it does seem to be contacting. This did not occur until I replaced the entirely dead rear shocks a couple months after I purchased it.

Due to this I have recently replaced the entire suspension (control arms and all), and the trans mount and still it persists. I have yet to do the motor mounts (power brake test showed nearly no play at all) or the u-joints (no noise or vibration, or play when I try to move it about by hand.

It is still using its original aluminum police driveshaft. There are no modifications to the car. Brakes are good. Etc. I am a trained tech myself and cannot find any other possibility other than maybe the body mounts, but I doubt they are so bad they would allow this to happen only under deceleration and light braking when loaded, or heavy when it is just me.