Steering Damper?
I've had this issue. I checked all bushings as previous posters stated and found that the steering damper was bad. I replaced the damper and have had no issues. Panhard rod bushings with also give you these symptoms. I have found the most success with LR bushings. I tried the OME yellow Poly and these failed after about 50 miles.
Lucas has since been upgraded to a D90 drag link with the OME damper located IFO axle up high with aftermarket crossover.
Next on my list are tie rod ends. Boo Hoo.
1990 RRC, 3.9L, AUTO "Willow Pond" (Sold)
1996 D1, 4.0L, AUTO "Lucas"
1999 RR, 4.0L, AUTO "Belle" (Sold)