front end shaking when brakeing.

Have the front rotors checked as it sounds like warped rotors to me

could be a broken belt in one of the front tires.switch the fonts to the back then test drive it.you could also jack up the front so both wheels are off the ground and grab the wheels at 9 and 3 o'clock and pull back and forth to check the idler arm as it can be worn out bad enought to shake the truck.