I am not getting into which one is more cost effective, but I will say I went from a 2013 Ram with Hemi to a 2014 Ram with Cummins and I couldnt be happier. yes it costs more, and maintenance will be more, but the mpg is certainly better, the trailers are not moving the truck around, and the overall towing experience is just plain better for me...and that is worth the additional cost to me. I didnt buy a 68k truck to worry about mpg's...I wanted a better towing machine and I got it.
The torque of a diesel is just a way different driving experience than a gasser...the gasser has more seat of the pants feel to it when you step on it, but the diesel builds power like a freight train....smoooooth...