So you're running 2" of lift, any other mods? Caster correct? Toe checked?
I was looking at this photo:
And a small lift to the panhard looks like it could help, but only 15mm or so. I'd be surprised if such a small adjustment made all that much difference.
You can readily isolate the effect of bump steer by bouncing the front of the car on level ground (stationary) and observing how much the wheel swings. Leaf sierras have terrible bumpsteer checked this way but drive OK. My own car has a similar relationship to a Jimmy (drag link/panhard) but barely bump steers at all.
Another test, drive over a speed hump square on with enough pace to get the suspension to cycle a bit. if its bumpsteer as bad as you say it is, the steering wheel should swing wildly. alternatively, if you "lock" the wheel with your arms, the car should dart left or right. (right, I think)
30˚ of steering wheel movement really sounds like a lot from driving on a tarmac road. This is why I'm suspicious it's not all/primarily bumpsteer, and might be due to another factor. What rims/tyres are you running? the leverage of heavier wheels/tyres/offset rims might be pulling the steering in the direction of the bump as the wheels encounter it. this will make it feel like bumpsteer. How is your kingpin preload/wiper seals - if these are loose you could be getting excessive tyre deflection (self steering) on bumps.
If you have aftermarket wheels/tyres with non-stock offset, can you try a set of stock tyres/wheels and drive the same route to see if it's reduced? My guess is it will be. Likewise, it doesn't take long to swap springs, can you put the stock springs back in? bumpsteer isn't related to lift height, only axle path, so it shouldn't get better with the lower springs. if it does, my guess comes back to my original call - a steep panhard angle transferring lateral force into vertical force and pushing the body around. I think any other factors are combining to make the car squirrely.
