2007 Honda accord Sedan LX 4 cylinder breaking issues?

Recently I've been noticing a a few problems with my Accord. It has around 110,000 miles on the meter. I first noticed the problem when I was driving to Las Vegas, on the steep downhill some 20 miles south outside of Vegas my car shakes as I break. I checked my rotors, the pads, flushed the fluid, did an alignment and a tire balance and rotation before I left, also changed the tranny fluid and motor oil and spark plugs and even the struts THE WHOLE SHEBANG. When it shakes, it doesn't actually shake the steering wheel like it does when the discs are warped instead its like this deep agonizing shutter that reverberates throughout the whole car. I even applied the handbrake for a section without the touching the pedal and the car still rattles. I even took it to a track, paid the entrance fee, ran my car up to 90+ and broke hard to see if it rattles on a level surface, NOTHING, it breaks fine on my brembo non slot not drilled with original Honda pads. Soon after I started to notice when I drive through a road that isn't pristine meaning there are cracks present in the asphalt but no potholes or anything that would hurt a car I hear a clanking sound similar to a bag of metal tools that bump around.

Someone Please help!

ALSO

i get 20 miles a gallon even though i did a chemical engine cleaning treatment

when i turn on my car it exhausts gasoline vapors

the engine groans on a slight uphill if its sort of stuck on 3rd gear because I'm not going fast enough

and I know a lot of Accord owners of my year with the same issue, MY RADIO IS BROKEN.

but apart from all of those above listed issues the engine runs beautifully.


I know I have a lot of issues, and its not like i neglect my car, which I really don't, its just every time I bring my car somewhere to get checked they do a test drive come back and say its nothing. I maintenance my car at every chance I get keeping everything original or manufacturer recommended stuff, I even change the air filter when I do an oil change, just to exemplify how much I care.