What is causing my truck to vibrate severely or shimmy when going thru a left hand curve to the point the wheels actually wobble?

i don't know. you might consider switching front tires
to see if that helps. also try rear wheels for testing.
unlikely but perhaps by moving a rim from 12 to 6 position [ or similar] on rotor may have very small effect.

Sounds like a wheel out of balance,tire low on air, tire belt shifted (starting to go), loose wheel, bad wheel bearing. press the helpful button and check links below
Diagnosing And Repairing Wheel Vibration

Shakes and Wobbles

ancient car needs alignment fast it might need only adjustment

start with tires; rotate them front to back

then check suspension components; anything loose will cause shimmy of any kind

brake rotors can be warped as well

if the wheel alignment is faulty ( castor wobble ) at 70 mph there is no way that you can describe it as a vibration as it virtually rip the steering wheel out of your hands. If it is a torque converter problem then at around 3850-4025 rpm stationary there will be a vibration of the vehicle and engine The sort of vibration that you are experiencing at 70 mph will come from a drive line problem. If rear wheel drive then it could be faulty "U" joints, worn slip joint or failed rear engine mount
If front wheel drive it may be cv joints or bent drive shafts,wheel bearings or brake callipers not moving freely on the mounting bolts.

Have your tires checked for tread separation and your wheels checked for balance. Out of balance tires will go through harmonics such that at one speed it will vibrate a lot more than at another (higher or lower) speed.

I would suspect deformed tyres ,they do go out of round with age and the sun which does wonderfull to tyres

Alignment has alot to do with the tires not shimmying.. Like zero toe setting. Loose componants like tie rod ends and the idler ar worn. You can ck for excess front end play by holding the front and back of the wheel and pushing and pulling on it, like rocking it. OR have someone rock the steering while you watch where the play is from underneath. By rocking I mean turn the steering wheel back and forth. Look at all th joints and pivot points for excess play, which is, movement not immediate to the rest of the steering system. Tire balance is very important. Wheel hop is a sign of a bad tire and it overtaxes the shock absorber. Shocks don't cause shimmy because they are a vertical movement controlA shimmy is lateral or side to side.Wheel balance weights must be spit. If a 2 oz. weight is needed to balance the tire, Oe once should be on the inside of the wheel and one ounce on the outside directly across from each outher.. Loose wheel brgs will cause shimmy, but they would not last long. Caster setting on the wheel alignment will also cause shimmy. Like on a shopping car. too much caster causes the wheel to start fluttering and is very hard on other componants. This may be why you have worn tie rod ends and a bad pitman arm. Worn control arm bushings and ball joints directly affect titre wear and can only be feltwhen the front end hits a dip and detected by side wear on the tire edges. Summary: replace the tie rod end and have the car aligned. Good Luck, -Ned_ sorry about the book

HEY I HAVE A QUESTION YOU DONT FEEL THE PROBLEM WHEN YOU HIT THE BRAKES AT HIGH SPEED IF YOU DO THE PROBLEM IN WHIT YOU BRAKES YOU NEED TO DO NEW SURFACE IN YOU ROTORS AND PUT NEW BRAKES

Hope I can help...but you have conflicting symptoms. IE... front end vibration but no shimmy in steering wheel?
Let me tell you this: If you feel the vibration when cruising(no brake & not accellerating) @ 60-70 mph; then 95% of the time it is in the tire/wheel/balance combination. (I know you said they were new but could still be out-of-round)