Check the drag link joints to see if they are starting to go bad. Just had a similar issue with a slight wobble in the steering btw 50-60 mph. I rotated tires had them rebalanced to eliminate tires as an issue. Did the planman video check down and found there was a slight snap in the drag link knuckle side. Not perceptible visibly but noticeable with a hand on the joint when turning the wheels back and forth. The joint was starting to go and I could feel the wobble in the steering wheel long before it was visibly shot.