Car shakes at high speeds

The other issue may be bent wheels. The stock wheels are so easy to bend one good pothole.

The best way to check the wheel for out of round is put the car on a lift and install the suspect wheel on the rear And then with car in the air spin that tire by hand and look for run out or wobble.

Really easy to detect run out that way, while ago I was chasing the same issue vibration at speed and
My usual tire store couldn’t figure it out bought new tires same issue. Went to another tire store and that tire tech figured it out using this method in about 5 minutes. I had 3 bent rims 1 was really bad,
Apparently my wife’s hobby is finding big holes in the road and hitting them at speed.

 

bought her with a salvage title.
could be many things.

I hear a thump whenever I let go of the gas peddle and right away step on the gas again
your control arm(s) are bad.

 

Just to say, Gen2 Prii in good condition have probably been known to get up to 100 mph smoothly, so of course something wrong here.

 

I hear it does take a little time, but definitely possible.

 

Have you tried changing around tires yet? You have been getting a lot of suggestions but you have not mentioned trying any of them.