O.K. here I go---2010 4WD, Ram CC, 5.7 Hemi, towing a Cougar 24rks with a gross weight of 10,000 lbs. First off, we've never even came close to maxing the trailer out (3300lbs for taters and undies) and overall average under 10 MPG. Our truck has 25,00 miles on it and over half has had the trailer on the back.
Personally, I think the *%^&$ gas we have to purchase is killing the mileage. We've tried higher octane with a small increase in MPG, but really nothing to sit up and take notice of.
When we haul the trailer, I figure 1000 towing miles will cost $500.00. Over a year, somehow that number is pretty close. I just don't look at the onboard computer anymore because it gives me heartburn.
See ya out there