Looks like the only thing you didn't do was install a panhard rod. Sounds like you don't need to at this point... that's great!
Based on the research I've done it seems like this the solution that points most directly to the minor issues I see on my E-450. I don't see that many folks install them though. I have a feeling that all of these solutions (sway bars, centering devices, etc...), while best at solving one handling issue, also overlap and address other issues as well.
Here's an interesting write up I found a while back on it for others reading this thread.
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