You may aso want to look at where the steering box is mounted,usually cracks and lets the box move,had serveral of these trucks and even seen brace made across frame for support generally speaking i would start there ,then coupler,after that check ball joints(especially if it flows grooves in road or darts from side to side after hitting bumps) hopefully tech checked ilder arm,etc
Must be a pretty common problem with those old trucks. My '77 has had the front frame boxed along with welded tabs on each frame rail and a 1 1/4" tubing brace bolted across. It was done right at the (rebuilt)steering box. Also someone put in a sway bar, poly strut rod bushings and looks like the control arm bushings have been tinkered with. Got this truck a month ago and still finding good stuff on it.
