[denisond3]

I think you have more than one problem, not surprising with many miles on the truck.
The 'lunging' when coming to stop could be a warped rotor or one with a bad spot in the casting, or maybe the wheel bearings need to be checked for being loose, i.e. not adjusted right. This is hard to check without freeing the rotor from the embrace of the pads. Try squeezing the caliper pistons back in 1/8th" and then check for wheel bearing 'play'.
The shimmy at 40-ish speeds is due to some imbalance or non-round condition of a front wheel or tire, probably made worse by lack of toe-in or other alignment change that is normal with miles and years. It could be a tire with some bad cords or a delaminating tread, or that has lost a balance weight. Try swapping tires from the back to see if the problem changes. It could also be a wheel not mounted flat to the hub, or a bent wheel. If your front suspension bushings are deteriorated (such as oil soaked) it would allow the shimmy to be more noticeable.
Getting the steering box adjusted would also help the shimmy, and help vague steering in general. I dont know about Fords steering boxes, but they are ALL adjustable, and should be adjusted about each 20,000 miles, or the truck wont steer as sweetly as it did when new. Both the steering shaft and the pitman shaft have adjustments, and both of them should be slightly 'pre-loaded', enough to eliminate any play, but not enough to cause noticeable binding when you are turning the steering wheel. It may be able to be done on the vehicle, with the usual limited access due to other stuff being in the way.
Good Luck