Dodge has online tables that will list all of the possible variables others have listed above...and give you the max ratings. Even 20" tires vs 17 can impact your ratings. On a personal note I had a 2004 4x2 quad cab with a hemi and 3:55 gearing and I regret not having a more "towing friendly" gear in there. As mentioned before, having too much truck is rarely an issue so the 3:92 gears will perform slightly better than the 3:55 with all other factors being the same. The only downside is worse mileage, but that's a compromise we face with towing houses down the road.