A 6.5 engine. All gas 1500 Subs are light duty. All 6.5 1500 are basically 3/4 tons. 8 lug wheels, big brakes, etc. As stated, 2500s have full floating rear, 1500s don't. Also 1500's have a small air dam, 2500s don't. 2500's have slightly higher GVW. Other than that, about the same. Oh...