Squirrely Avalon 2006 caster question

[fixittony]

Eager to find a way to improve the poor directional stability of my 2006 Avalon at highway speeds, I asked the dealer to set the caster as high as possible (within spec) only to discover that it was not adjustable. It sits at about 2.4 degrees. This struck me as rather low and a likely source of the squirreliness and annoying light steering. Everything is in spec, and it only has 15K on it.

Does any one know if Toyota is pondering a fix? Is it possible to adjust the caster? Is there a way to start a discussion with Toyota?

I just got the transmission reflashed after waiting 1.5 years, but at least it was a fantastic improvement. It would be nice to make it a solid highway car and not have to wait another year.