Joe- Yup, shim some more caster into that thing. The kingpins are standing up too straight. Need to lean them back (top of kingpin towards the back more) a few degrees and road test again. Any good local truck alignment shop should have the shims. Keep playing with it until you get it to feel right, I can't give you a magic number to shoot for. Too much caster (like a rail dragster) will make it track straight, but turn hard because the wheels are trying to "flop" over when you turn. Too little caster (kingpin straight up and down) and it will turn easy, but wander and not seem to have a "home" position.
