It's PROBABLY warped disk brake rotors. Brake rotors will warp when overheated and if you go downhill very often, they've probably overheated.
Replace the rotors with a high quality product and they'll last longer.
Warped rotor(s), due to too much hard braking (or braking for too long, like when going downhill). You can replace them or get them shaved so they are flat again. Break sooner and not as hard will prevent them from overheating, which causes them to warp.
it shakes to the right or left
usually steering shakes over 60 mph is due to front tires needing to be balanced unless you have something more serious going on.
You may have a ball joint going out or your wheels are unbalanced
check the balancing on the tires.
we could go about 35mph when not going downhill you can go 28mph
Have your tires rotated and balanced. Make sure they inspect the tires/wheels for any damage.
Milk Shakes! They are always going to the resturaunt to have milk shakes.
No the can go faster downhill or uphill
If they were backing up, they would be going backwards... If they were braking, they wouldn't be going anywhere......
No
Your brake might grab when going downhill because the pads are wearing out. The lines may also need bled properly.