A much better suspect is a lower control arm bushing. In particular, look at the cross member where the bushings are attached for signs the bolts have been sliding back and forth. You may not be able to replicate this with a pry bar. It may be necessary to remove the control arm to inspect the mounting holes in the cross member.
The tie rod ends are pretty close to being in the same plane as the lower control arm, so when the control arm shifts and makes the lower ball joint move to the left or right, the steering linkage needs to have its length changed the same amount. Since no alignment technician is running alongside the truck to do that, the mismatched length turns that wheel left or right, and you have to make the two front wheels equal by turning the steering wheel. That is why it is off-center at times.
This may not be practical, but if you can get it in the off-center condition and keep it there, another alignment check will show which wheel has the problem.
You also could have an upper control arm shifting position but that will have almost no affect on the steering wheel's position. It will cause a pull one way though. By 1993 most GM trucks had upper frame bolt holes that had to be cut to an oval shape with a special tool to allow for alignment adjustment, and blocks were removed and cam washers were installed. They could not be bothered to do that at the factory, but that is what is needed to make it adjustable. It is possible one of those bolts was not fully tightened and the control arm is sliding back and forth. Rust can develop in the threads making the bolt appear to be fully tightened when it really is not.
Wednesday, May 18th, 2016 AT 6:01 PM