I guess it depends on where you look. This page, http://www.ramtrucks.com/en/towing_guide/, lists the Crew 4x4 Laramie at 7200lbs for 3.55 and 7450 for 3.92 and a Tradesman 4x4 all the way up to 8550 w/3.92
Ya know, you are right. I remember up to 9200 for the 2wd model. Mine is a 4x4 big horn with 3.92 no slip. Good catch. There were a number of different combos all with different tow capacities.