The leaf springs have never been replaced. Think that has anything to do with the handling?
Weak springs will allow the axle to hop all over tarnation instead of resisting the hill or valley that the wheel goes over.
How many miles would you estimate your truck's suspension has on it?
Anti-sway bars do their work while in a turn. Shouldn't have much effect at a pot hole.
Yes, a handling improvement of any kind would be welcome, I think.