Q: vibration clunking sounds and shaking when the car loses speed, has less rpm or brakes applied

my van is making clunk and vibration noises that go away if i am gaining speed and rpm but becomes severely worse when the rpms level out at a travel speed. it also worsens when coasting. when the rpms are low the vibration is high. it is strong enough that i feel it in the floorboard and the steering wheel as well as in the cabin of the van in general. It becomes louder the slower you coast and almost violent when the breaks are applied at any speed. the front tires have been replaced and balanced, the brake pads and rotors have been replaced and re-inspected, Inner and outer tie-rod ends have been inspected and do not appear to be the culprit. the speed of the vibration and thunky noise increases as the vehicle loses speed via disengaging the accelerator pad or by applying the brakes. But if you accelerate quickly is subsides again until you begin to lose rpm and speed again.

My car has 225875 miles.
My car has an automatic transmission.