I had the death wobble on my Ram when it was almost new -15,000 miles.

The shocks were new Bilsteins and the rest of the suspension was stock as well as the tires.

More positive caster fixed it...

PS If you've experienced "death wobble" you'll understand why the name is accurate. Mine was at 85 mph Steering the truck is impossible until the wobble stops.

I suspect it only happens with the wheels pointed straight which is lucky for us and points to an alignment problem. Worn suspension parts probably make it occur more often as Dave said.