My 2000 f150 has 39989 miles and the brakes are acting up. When i start braking from speeds of 45 and up the vehicle shakes, and the pedal goes further down at all speeds, i looked at the pads and rotors, they look fine. any sugestions were to look now.

 

Have your front rotors turned. Some Ford rotors are not very reliable.

 

With that age and mileage you are probably due for your first brake job. The pulsation is coming from the rotors, DTV (disc thickness variation) I'd get the rotors turned and put on a set of ceramic pads, and they help prevent DTV.