They'll definitely settle down some. It'll probably take a few months though. I had a set of the 3,600 lb SS springs on my Challenger, which I replaced with regular XHD springs after awhile. Currently I'm using the 3,600 lb SS springs to hold up the back of my Dart and keep it a roller. Even it doesn't sit up as high as your Duster does.
A set of 1" lowering blocks is an easy solution, although you'll need longer U-bolts to go with them. If/when the springs settle down some you can remove the blocks.
