I don't think you are too far off. I have a 2015 Laramie crew cab, since new I only manage to get 15-17mpg empty with a mix of city and highway driving. Pulling my Jeep on an open trailer (maybe 6000 lbs) I would get 11-12, towing a 4500lb travel trailer I would get 10, amd with my current 6500lb travel trailer, I'm right at 8.5mpg. The truck has 104k on it, 48k have been with a trailer hooked up. I go through at least 1 set of exhaust manifold studs a year, I am assuming from the extended towing and heat build up. Other than, just routine maintenance. I put spark plugs in it not too long ago, it didn't make any noticeable changes.