[hotwheels]

Sounds like you have several different things going on........First, if you get into the habit as most of us, you will tend to be fairly aggressive driving your stang. This will tend to wear out the pinion seal and cause a slight leakage. Just from the constant up and down action of the axle housing........So i would think if you change that seal, that will cover the leaking.

2nd, vibration could be caused by several things like a bad u-joint, out of balanced tires, or a bad engine dampner. So, did the vibration start before the tire rotation? when the did the rotation, were the tires rebalanced? I would think at 70mph, it's a tire issue myself and this is where i would focus most of my attention.........on the u-joint just jack up the car, and grab the driveline right at the joint and move it up and down, watching the joint. If the joint moves fairly loosely, you will need to replace the joint. ( i wouldn't think your joint is bad yet, but you never know.)

3rd, Shaking when applying the brakes is almost always a warped rotor. Depending on the miles on the car, just pull off the front rotors and take them to a shop that can turn them for you and make them smooth again. Depending on your money.....Usually about 10 bucks a rotor. If money is a little free, just order some new ones. Try to stay away from the ones with holes drilled in them though, they tend to get cracks in them....The rotor type that have the grooves in them are a good rotor if you want a set that atleast look kewl.

Lastly, your engine dampner which is a little harder to diagnose. But these are a common failure on mostly 5.0L cars and tend to cause a vibration through the entire car at all mph......Usually not noticeable at idle. (Don't go after this first do to cost of a new dampner)......