Trailer Life "Guide to Towing"

It's simple math. That combo of engine, transmission and rear axle is identical in all three trucks. They all have the same GCWR. The 3500 series trucks are slightly heavier empty, therefore they can tow slightly less weight. The higher payload ratings make the 3500 a better choice, although apart from rear suspension there is very little difference in the actual trucks, as evidenced by the minimal difference in empty weight.