I just got back from a 3000+ mile road trip and the fastest big trailer haulers without a doubt are duramax's. I was cruising the speed limits ie 80mph and duramax's flew by me pulling big 5th wheels like I was standing still. I never got passed by RAMS or Fords just Duramax's....I went from Western Montana to South East Minn thru both dakotas and Wyoming and I noticed a lot of new RAMs doing utility type work ie fires, oil/gas and agricultural type stuff. By far tho more GM trucks pulling big camp trailers and 5th wheels and seemed like Ford HD was hauling more slide in campers.