My current Duramax has the 3.23 rear axle. The motor has lots of torque and I have never been wanting for power to pass or merge. Have not really towed anything heavier than a couple of SxS with it but that is not what I bought it for, my daily commute is 28 miles each way so I got it for the mileage. I recently towed a SxS on a single axle trailer out to a friends place, 200 miles, averaged 19.7 mpg
