That is a big issue, lots of possible causes. You need to have soemone carve the steering wheel back and forth while you look at the track bar (both ends) and the tie rod ends to see if there is any slop in any. The track bar is the primary connection holding the axle centered under the vehicle- it uses a replaceable bushing at the axle end, and a non-replaceable tie rod end at the frame rail. After these, next check the ball joints by rocking the tire at 6:00 and 12:00 oclock (off the ground on jack stands). Last would be the control arm bushings. (This is the order they wore out on my 1990, all have been replaced- on the third track bar.)