i'd go with shocks bottoming out, the springs wont have really changed to much in the stiffness as you haven't added any leaves or changed any, stock shocks would in no way would cause that much of a jolt due to compression rate being too high.
maybe unbolt your shocks from the bottom nount, cable tie them out the way and go for a drive over said 'calming area' and see hou it feels, if no sudden jolt start your search for some shorter shocks :)