Here is what you need, you can get them at NAPA as well as the supplier in the link.
http://www.chevsofthe40s.com/browse.lasso?&dept=Truck&cat=190T&skip=18

(next part up and down are more wedges)

My truck drives 100% better since adding a 2 degree. The factory setting may not be right any more if you changed the ride hight or front to rear angle. Start with 3 and reduce down if it to hard to steer when setting still. It will try to lift the truck when setting still if you have to much caster. Another way to tell if you need more is if the steering wheel doesn't return to center after making a turn.

To install them just loosen the front u-bolt with axle hanging, and slip them in. You should notice a change right off.

Joe