Congrats on the 2011 ram, I like the new looks of them and i have thought about trading in again, but I am tired of making payments, so for now....I just look. LOL. Anyway, it's my opinion that you could probably do better than 10mpg on a consistent basis...at least prior to going into a regen. Over the last few years, I've subscribed to a cummins forum and tried to learn as much as I can about our trucks and I think you might find some helpful info there too. But I wanted to mention to you that under my own findings, if I keep the rpm under 1900 at all times...and do my best to keep the turbo from pushing over single digits, you can get some pretty surprising numbers. Around here, it's pretty tough to keep the vehicle under 70mph due to traffic flow, but the last time I made a road trip (empty), I kept the cruise at 68mph and achieved a 20.18mpg on that tank. The worst I've done pulling the roo is 14mpg, but that's going over 4 different mountain passes stretching from northern Colorado to southwestern Colorado. Granted, I'm not pulling your specific trailer nor do I have same specs on the truck, but I think the principle would be the same...might be worth a try and see how it goes.
(before my comment on my fuel mileage starts a whole new conversation, I'll just say that I eliminated as many variables as I could to get the most accurate reading that i could and added it to a years worth of stats that I've kept.). Oh and last I read, the overhead console reading still isn't accurate to any extent, so I wouldn't rely it to tell you the truth.
Where we've been:
2000 Rockwood Roo M-18 Hybrid
2006 Dodge Ram 2500 Auto 5.9 Diesel
Gone but not forgotten -1986 Rockwood 1003 PUP