Boarderguy
Chief Narctopus Wrangler
And a 450... heavy chassis and gearing is more optimized for towing vs cruising. Our 3500 denali gets 21+ highway, 11-12 towing a 10.5k trailer, and 16 ish city.Being a Dully and in the mountains is also not helping that! Are highway speed is 80 also I am sure if I was in flatter land it get better and slow it down a little.