The shim suggestion is right on for a caster adjustment, but there is no camber adjustment for the I beam axle on the GM trucks. If camber is out, that means the axle is bent (unlikely), and GM does not suggest bending to fix ( Ibeleive it can be done, with proper equipment and a knowlegable mechanic working on it). One problem with using the shims is that thay no longer produce the 2" shim that fits the light truck (no demand), but the wider 3' ones could be cut down to fit.
BTW, I have read that article, and agree with most of it. However, on the 8" rim part, there is a failure to suggest the other cure for the problem. The tire mentioned in the article (as well as what you have on your truck) are actually too narrow for the rim. That size tire is better suited for a 7" rim, not an 8". So the other option would be a wider tire, perhaps a 255/70/15, or like what I have on mine, a 30x9.50x15 C. That will correct a wander. due to a rim/tire mismatch. Same applies using a wide tire on too narrow of a rim. The rim must support the sidewall correctly for proper handling.

Bill Burmeister