I'll beat the tom tom on diesels. I have a 2500 with the CTD and tow 9000lbs. 3.73 gears. I wouldn't have it any other way. Yes a gasser would get me there and back but having enough reserve power makes it much nicer. I feel the 2500 CTD and my 9000lb 5'er are a perfect match. Sure the Ram is rated to tow more but so are most trucks with what people tow with. I get 10.5-11.5 depending on conditions. I will see 12mpg with no wind doing 62mph. 17-18mpg empty.
JMO, but I would skip the 5.7 and get a 2014 2500 6.4 Hemi if your serious about a gasser. IMO the 5.7's are gas hogs and the new 6.4 should be better with more power.