Front End shaking/hopping

I have a 93 cherokee 2wd 6c 4.0l. The problem with this vehicle occurs at relatively high speeds (in excess of 50mph). When a single tire of the front end hits a pothole or expansion joint awkwardly in the road the front starts shaking and hopping violently along with the steering column vibrating. Once this occurs I have to slow down and pull off the road and then back on. I have recently replaced the tires and steering stabilizer but to no avail the problem persists. I have also had a few mechanics take a look at it. I have been told everything looks fine and tight. One thing to note is this vehicle has extensive exposure to salt and is pretty rusty underneath. Possible metal fatigue? I have also noticed the problem seems to not occur when the tires are fully inflated, but this could be my imagination.

Any ideas? All serious replies appreciated.