Go to Shock Therapy and check out their video's on the XX. I use their coils and it made a big difference. The stock springs are OK, but a little too soft. Plus they will keep sagging as they break in. Shock Therapy claims that you only have to adjust their springs once due to break in sag, but I never had to adjust mine?
Copy that. I used the videos on the initial setup, and it helped quite a bit. I am setting up a different car now that is need of revalving. My plan was to compare the stock shim stack/ spring rate combo to my current spring rate and see how far off my valving is.