I was getting 13.5 this past winter with my 2016 Crew 2500HD. That's a mix of city and highway driving along with a lot of stops at customers. Usually loaded fairly light. I just took a 300 mile trip yesterday and set the cruise at 75 MPH. I was happy to see 14.5 MPG after that ride. I thought the speed would hurt that number a little more.
I had a noise when taking my foot off the gas and the truck would start to slow down. It seemed like the truck was fighting and the rpm's would seem high. At 600 miles, I took in and found out my transfer case was bad. There was a retaining ring that failed and allowed a bearing to move. The dealer fixed under warranty. I have the manual floor shifter.
Don'f forget the added expense of the motor itself at the time of vehicle purchase. I agree 100% with you....buy because you want one or you tow heavy and often.