Shakes terribly when brakes applied at highway speeds?

Warped brake rotor usually cause high vibration at high speeds. But you can also feel it at lower speeds. But bad ball joints and tie rod end will cause vibration at high speeds. Ball joints will pop at pot holes, sometimes. Tie rods can be felt in the steering wheel at a stop. Move the wheel slightly to the left and right, you can feel/hear a tap as you turn it.

have the rear suspension bushes checked out including the shockies.
I would also suggest a rear end wheel alignment and a wheel bearing check

you might have a bad front rotor ...warped or burnt ...I would check there 1st

Sound like your front rotors are warped. Replace the front brake pads and rotors and that should take care of your problem. 4 thumbs up is appreciated if this helps.

i do believe you mean the service brakes, and when pushing the brake pedal the truck shakes?

Pad transfer will cause uneven brake discs with humps on em. Every time you then step on the brake pedal you'll feel the pads going over the humps, causing the shakes.

The best way to get rid of this is to replace the disc brakes with new discs.
Remember to change the pads too.

more than likely you need to have your brake rotors resurfaced or replaced

Your car has front disc brakes, the disc's are running out of true, as u apply the brake this causes the steering wheel to shake, the higher the speed the more u feel this, the solution is to have the front brake disc's machined true again on a brake lathe or if they are to thin replace them.

You seem to have more than one problem, first of all the balding tire you have a negative camber problem that can be adjusted by getting a wheel alignment done. The shaking problem while applying brake could mean that you have bad/warped front rotors. It can also mean bad Tie rods. Lastly it can mean that the front tires needs to be high speed balanced. Good Luck

Anti-lock brakes mean the car shakes when the brake is applied. Try pumping the brakes.