I'm having some trouble with my truck acting a bit nervous at speeds above 55mph.
It started after I changed my wheels and tires up from the stock pizza cutters to 19.5" commercial.
The larger tires really brought out the fact that my steering componets were shot. Tie rod ends pitman arm drag link and track bar were all replaced. I tightened the steering box as well, this took all but about a 1/8" - 1/4" of play out of the wheel. This made a major improvement in the wandering I was seeing on the highway, but the truck still has a nervous twitch every once in awhile at speed.
Even with the warn steering links and drag link the truck had perfect manners on the highway before.
I'm starting to think that it may be an alignment issue. When I replaced the steering components I set the toe angle to factory spec which is very near 0 deg. Now I've allways thought that you had to have either a small amount of toe-in or toe-out to promote good straight line tracking. But with the factory saying otherwise I set it to 0 deg.
But with all new components and a tight wheel, I'm leaning towards maybe dialing in a small amount of toe-in to see if it will settle the trucks nervous steering at high speed.

Any thoughts out there?

Original tire size: 215/85/16 Michelin LTX E load range
New tire size : 225/70/19.5 Goodyear G647 RSA F load range

 

Try 1/8 inch tow in.
Check the caster---5-6 degrees and the camber should be very close l + r.
This is what I did and it drives nice. It could use more caster to help it stay straight.