1995 Jeep Laredo Violent shaking when hitting bumps.

The jeep was sitting for about 6 months before I bought it just a couple weeks ago. It has a Skyjacker lift kit and larger tires.. Since having it, there have been about 6 times when I would hit a bump that would spark a rash of violent shaking from the front end. I need to slow down to a almost a stop in order to stop the shaking. This doesn't happen most of the times I hit bumps. I can go on the freeway with no problem, or go down a bumpy road without problems. But out of nowhere, at about 30 mph, I can hit a particular bump and the shaking will start. Once it happens it generally doesn't happen again, except a couple days ago where it happened three times in a row.
There are no obvious problems with the front end. Yesterday I lubed the front end because all the points were dry, but it seems like it is a bigger problem then that. Any direction or suggestions are appreciated.