I have a 2012 JKU Sport with auto. My build sheet says 3.21 rear end and lists auto farther down the sheet under options. I've read in several places that the autos only come with at least a 3.73. I check what's stamped on the diff cover and it doesn't match anything to do with either. Anyone know how to tell for sure? Just curious for towing purposes. Dealer says I'm good up to 2,000 lbs. but Chrysler charts say 1,000 lbs. with 3.21 rear end.