Taco Bump Steer? Where to Start?

I would want it to be at least 3 degrees. If your truck is lifted and you do not have aftermarket UCA's, 3 degrees might not be obtainable. On my truck with 37's, I run about 4 degrees. When my truck first had about a 3" lift with no aftermarket UCA's, it would wander on the freeway when hitting small bumps, caster #'s were at the lower end of the acceptable OEM spec, and that was with about 33" tires.

 

And, wandering can also be caused by having any play in the steering system to the tires, steering shaft, steering rack, steering rack bushings, inner and outer tie rods, bad wheel bearings, etc.....

 

Your toe numbers are very low. This will cause instability over bumps (wants to dart rather than being stable at center). Get at least in the middle of the range for total toe.

 

Thank you. I’ve replaced all the ball joints in an outer tie, rods, rack and pinion steering intermediate shaft, sway bar links, and sway bar bushings. Tires are brand new and I’ve got a regular factory spec alignment. I think the caster sit at about 1.5-2.0

 

Those large tires can exacerbate the wander / tracking issues for sure . As others have said maxing out the caster will probably help. FYI Most of these alignment places won’t touch the adjustments if it’s in spec, so good luck.

btw, you asked before about bumping up the 5100s; that will limit your ability to get enough camber without aftermarket UCAs, so that would make it worse.
You’ll notice folks with tires and lift will also do UCAs primarily to get more caster. (Myself included, and it 3 degs helped tremendously)