I got my 2500 in August of last year. I have 32,000 on it. I have towed my 31 travel trailer a few times with it, did as expected.
Likes: Integrated trailer brake system, exhaust brake, plenty of power, remote start, A/C controls are better than my 2006, easy to shut tailgate (light feeling), no exhaust smoke, quiet, 265 tires instead of 245's, mileage around town 16.5, on the highway at 75 - 80, 17 - 18, towing pretty much any of my trailers 12 - 14, if it would go slower, mileage would probably increase some.
Dislikes, compared to my 2006: The biggest is the steering wheel controls are not user friendly, the outside temp guage has issues, but Shaun told me that it is working the way it was designed and more importantly how to re-set it when needed, no exhaust smoke, no A/C vents for back seat, seats not as comfortable, lack of side pockets/storage areas inside.
The DEF is not that big of a deal to me. I normally change my oil when it gets to about 50% which is normally around 5,000 miles. The tank holds 5 gals of DEF, I usually put in 3 to 4 gallons. It is not constant and seems to vary depending on the type of driving I am doing.
If I could have my choice, I would like the power of the new truck with the interior of my 2006.
If you have any questions throw them out there, I will try to answer.