The 2500HD had an available five-speed (six-speed for 2006–2007 models) Allison 1000 transmission with the Vortec 8100 and Duramax 6.6. The Silverado 3500 offered the same engine/transmission features that the 2500HD, however it was usually equipped with "dually" twin wheels at the rear and had a stronger suspension. The HD models were primarily used for towing and high-weight cargo. The Chevrolet Silverado 2500HD came in at #2 in a 2016 study by iSeeCars.com ranking the top 10 longest-lasting vehicles. The Silverado 2500HD had 5.7% of vehicles over 200,000 miles, according to the iSeeCars study.:)