I'd have to refer you to one of the Ram Owners' forums for accurate mpg numbers.
I watch BBCBoards.net, the big bass fisherman website, and Ram owners with Hemi engines complain often about fuel mileage. They don't complain about the engine otherwise, as it's very strong.
If you have to drive 100 miles round trip, you'd do best to keep driving what you've got for now. Or, go for the Cummins diesel as they're so capable of being driven mega miles.
If you're regularly towing 10K or more, go diesel. Less than 10K, the gas engines will work.