What kind of fuel mileage can you expect

We had a 2011 Ram diesel with 3.42 gearing and a six-speed manual, long bed crew-cab. Our only FW tow with it was disappointing, on the way to Zion we got around 12 mpg, then drove around without the FW to various places, and then came home. When we got home we were down to slightly less than 11 mpg overall. Pulled the boat to the lake to fish three times and mileage kept dropping. I don't know if it was me or the truck, but after nine months I gave up on it and got a different brand with which I am quite satisfied now.