Tires/wheels out of balance?
You have warped rotors. They will need to be removed and trued or replaced. Causes of this are lug nuts overtightened, or heat from heavy braking at high speeds.
This is a self-exited vibration problem.
Front rotors could be warped. Replace
Probably worn steering and/or suspension parts. Have the front end safety inspected.
Only at low speeds, or worst at low speeds? Either way it's probably a bad front tire. Failing that, bad front wheel rim or front wheel rim not properly secured to the hub.
Wheel bearings are the most common for causing a vibration.
Low speeds indicate shifted belts in the tires. If it also pulls to one side, try rotating that side front to back.
ball joints
have front suspension checked
If your truck is 2wd than check the bearing, hub assembly. This is considering that you have the balance and alignment checked at a shop already
Sway bar bushings
Switch the front wheels to the rear and try it; if the vibration has changed at all you have a tire/wheel problem. It is not uncommon for a shop to miss this problem. Most vibrations like yours ARE tire/whhel problems. sounds like u-joints