Certified ATF+4 trans fluid should be good for 4 years/60K under normal use. I would change it every 30K if you tow or drive in heavy stop and go traffic. FYI the 2011 GC owners manual states to change the trans fluid and filters at 48 months or 64K "if using your vehicle for any of the following: police, taxi, fleet, or frequent trailer towing" otherwise at 90 months or 120K. BTW the same transmission fluid is used in your van is also used in my 06 2500 diesel truck and its good for 3 years or 30K for severe usage like heavy towing so I see no reason why it would not hold up for 30K in your van. BTW if I was to drive my truck like a car the owners manual states the trans fluid would not need to be changed for 5 years or 100K.
Last edited by DBLR; 02-06-2012 at 03:54 PM.