I thought i had a problem with my leaf springs because the ride was getting kind of harsh on my 2001 xlt but it was a combo of things low tire tread left the heavier and stiffer suspension etc... im thinking about getting monroe sensa-track shocks in the fall which will soften up the ride a little bit, but as far as the leaf springs some people say lube them up so they can slide easier which may decrease the harshness of the ride which i have done, only with wd-40 which is a light lubricant and since leaf springs dont have any greese fittings there isnt much you can do....if you have a bad sagging problem take it to a ford dealer dont play around with mom and pop shops.