Our service truck at work is 2005 Ford F250, it came with a factory installed death wobble at highway speeds when you hit just the right bump in the road. We installed two additional dampers on the front for a total of 3. It cured it, but it makes for some really tough steering even with power assist. On a manual steer truck, I would not want to drive one very long with a damper installed.
A quick fix is pumping in the thickest grease you can find to tighten up steering and suspension joints. We used to pump in thick white wheel bearing grease in the front ends of buses to get through state inspections, if the grease tube wasn't warm, it wasn't going in, even when warm you about had to stand on the handle to get into the joints, but they were darn tight when you were done! It would be a good test to see if its the truck or the tires.
Grease grades,
https://www.itwprobrands.com/resources/blog/nlgi-grease-grades a 4 or 5 grade would really tighten up the front end.
