One or both front brake rotors warped.(overheated) take off and have both re-surfaced ("turned") or if beyond 'trueing-up' then replace them both. About 25.00 ea. (new)
At moderate speeds, yes. For higher speeds or tight cornering, you might be causing a problem.
Tires/wheels out of balance?
Alignment
Most likely its your tires. Could just need balanced. Or you might have uneven wear making it shimmy.
Probably worn steering and/or suspension parts. Have the front end safety inspected.
Because your motor is spinning faster at higher speeds causing higher rpm's
Only at low speeds, or worst at low speeds? Either way it's probably a bad front tire. Failing that, bad front wheel rim or front wheel rim not properly secured to the hub.
You have warped rotors. They will need to be removed and trued or replaced. Causes of this are lug nuts overtightened, or heat from heavy braking at high speeds.
The blower motor speed resister is burned out.
I was considering a Lexus RX400h when I realized that it was very inefficient at freeway speeds 65-75 mph. Most of my driving is freeway at high speeds. How does the Toyota Highlander hybrid technology work? Is it still beneficial/cost effective at freeway speeds?
Switch the front wheels to the rear and try it; if the vibration has changed at all you have a tire/wheel problem. It is not uncommon for a shop to miss this problem. Most vibrations like yours ARE tire/whhel problems. sounds like u-joints
Because at higher speeds you have more velocity than at lower speeds transferring more energy to make a bigger crashing causing more damage.