Let's trouble shoot this thing!
-Go to both corners and push down on the car... does it move?
-Have you checked the shock mounts... is something pushing through?
-Get under there... what about the sway bar mounts and their links, does everything check out?
-Control Arms... Thrust Arms..... Check, CHECK!
-This is going out on a limb... how do the springs look?
I'm in serious doubt that the new cartridges are out of wack. I was all pissed off at Koni because my back end was bouncing all over the place after 2000 miles... turned out that I didn't install a large washer on the top of the shock mount and it ripped everything to shreads! Be patient, check EVERYTHING and then get pissed off at Koni if it's their cartridge.
Good luck!
-Eric