If Your Wheels are aligned and brakes are good then there are a few things you need to check.
- Check needle bearings.
- Check if power steering is normal.
- Check if the lug nuts on the wheels are proper.
- Check your camber alignment.
I googled and it seems this vibration is a frequnt problem on the F150.
Usually it is the U-Joints which give way causing the vibrations.
You can check this by jacking up your front end, turn the steering wheel all the way to one side and spin your tire by hand (spin and let go). If it spins real nice then the ujoint isn't the issue. If the ujoint is bad your tire won't spin good or might even stop and go the other way.
Also, if you have any fine red dust around the ujoint bearing caps that is a sign the grease inside the ujoint is all dried up and needs replaced.