Dave,
One time someone that I know personally (very), put an axle in with the shims backwards so that the kingpins tilted forward at the top. Then, that person drove 1000 miles in one trip. The vehicle would change lanes on its own, it was a real chore to keep it in the lane on a two lane road. I er....he drove the trip without stoping. It was a real chore. After the 1000 miles, the caster problem was discovered..... quick fix, long-lasting lesson.

mike