2005 Chevy Silverado Vibration

I recently started having a vibration only when braking and usually only from higher speeds. I originally turned the rotors without replacing the pads. the vibration never went away, so I replaced the pads and rotors. However, the vibration still occurs and is still as bad as before. I checked the front end suspension and everything seems fine there. Like I said it doesn't vibrate all the time, mostly from higher speeds (above 35 mph). However, when it does vobrate it vibrates the whole vehicle, but can it seems like the vibration originates from the front. It will shake the floorboard the steering wheel as well as the seat. I am out of ideas on what the problem could be. Was told it could be the ABS Module but the light never kicks on. The truck runs smoothly except for when braking under high speeds. Hopefully you can help so I dont have to pay someone to look at it.