I have to think it is the shocks as well. I have the 8 leaf pack with soft valved 7100's, and it is pretty close to a stock ride. What is interesting is that you can put 100 lbs in the bed and then it is a smooth ride. I was amazed that such little weight made a big difference, but this is because of the shocks, not the springs.
I wouldn't recommend sending them to deaver for tuning as it would be a shot in the dark that they would be to your expectations, and the shipping would be very expensive for you to send back and forth from Illinois to Cali, till you were happy or possible unhappy. The 7 pack leaf should be a nice everyday leaf with a limitation on payload. My guess is you would lose 2 inches of lift with 400 lbs of payload, since my 8 leaf's loose 2 inches with 500lbs. They should ride real good with the right shock, and no wierd mounting bracket. I've seen people run too long of a shock and be bottoming out on the compression of the shock so the shock wasn't working.
Bottom line--Look into the shocks first.