sorry if this has already been covered Mark, but make sure the cars is fully loaded (battery in etc), then drop it from about 10 inches onto kitchen bench (which the wife will love) then measure the height. Adjust with the spring collars not the droop screws. About 20mm is fine. Higher will produce more grip, but with greater chance of grip roll. Lower the opposite effect. I found with the durango is not make to many changes at once, as it easy to create a car that's a pig to drive and you wont know why!
Has yours still got the gear diff? I found mine a pig with that in. Ball diff was much better.
Weights make a big difference too..
few handy vids here:
https://www.youtube.com/user/WatchTeamDurango/videos