Hard to imagine they even offer that gear in anything beyond a 2wd half ton. Buddy ran into same issue in his previous Sierra when he assumed tow package meant rear end gear to match. Based on how well my 2011 Sierra (342) would out tow vs my '03 with 373's, it's not always about the ratio but instead how much low / mid torque your engine makes. My current Ram with 321 will out tow the '11 by a substantial margin while using dramatically less fuel. Doesn't make my previous truck a dud, just new one does what I need better.