There seems to be an issue with the ISX650, reading over on the IRV2 Forums and there are quite a few threads on this subject. Best of luck with the help from Cummins. Great products but as with everything else there is a bad one from time to time.
DEF is the latest problem added to our diesel engines. All works well until you get a bad batch as in this post. DEF is both time and temperature sensitive. If you are down South and plan to stay a while do not fill your DEF tank, anything above 85 degrees shortens the life of the DEF and who knows what the temperature was in the warehouse before getting to the stores. 2 &1/2 gal. jugs are the way to go but check the born on date. My diesel truck does not have a way to drain the DEF tank.