Yeah, thats known as death wobble, not bump steer. Bump steer is when you hit a bump. and the vehicle steers. Death wobble is when the frontend starts shaking so violently you can't really hold it, and it doesn't go away until you slow down a good bit.
With that much tire (assuming 2-3" of lift), you probably have a worn out tie-rod end, or a loose trackbar bolt. Its fairly easy to check, look under the front of the jeep and have someone rock the steering wheel right and left while it is running. None of the junction points for the steering should show any movement side to side, and the track bar (runs from the frame on the drivers side to the front of the axle on the passenger side) should only have about 1/8-1/4" of movement due to the rubber bushing.