Jon G, I don't want to say you're wrong, but in my case the 4° caster shims helped out a lot with the handling of my truck. If it made it harder to steer, I didn't notice.
The 2° shims were designed for the original bias ply tires and it's generally axcepted that you need a bit more caster with radials.
Also, 60+ year old springs de-arch a bit, reduceing caster. I had 2° shims, but my caster was 1° positive.
So with 4° shims I'm running about 3° positive.
