Don't know, but by going to a 4.30 you up ur towing capacity up to 15000lbs vs. 12000 lbs. On fifth wheel towing. Why would someone buy a 3/4 or 1 ton truck rated to pull only 12000 pounds. If I do go back to gas I'm definately gonna have to order one with 4.30 gearing. Drove one today, and at 60 mph with 3.73s it almost seemed like it was lugging the engine, drop down to 5th and the milage was about the same, better going up hills according to the display!