Usually at high speeds (freeway) when I break, I can fell the steering wheel and brake pedal shake. Anyone know what is causing this?

 

that would usually be warped rotors. or other things in the driveline axles, maybe you need an alignment.
if you have slotted rotors it will also do that also. i rember when i had slotted rotors you can feel the brake petal vibrate

 

Read this about 'warped' brake rotors...

http://www.stoptech.com/whitep...h.htm

 

i agree with all above and have another set of solutions, 1 would be tires, i had low shitty tires and the vibrated when i tried to brake alos if i braked harder they slid that was so fun, 2nd is bent rims one of my steelis was bent from a curb from the owner before me and when i braked that side vibrated and it made the steering wheel, otherwise an alignment rotors, slotted brakes, it could be alot of things