I don't know if I comment on your posts before but I think I have.
The ONLY issue I have with you getting the diesel for daily driving is the fact that the emission stuff will eat you alive.
My experience is limited to the 2012 6.7 but the 08 is basically the identical setup. If you don't tow heavy or drive for long periods of time often then the truck will be doing more regeneration's to keep the DPF filter clean. Basically for your consideration that 12-14 MPG is a very high guess. If the truck has to constantly clean that filter you are looking at 9-12 MPG.
If you can get away with doing deletes then more power to you.
I am not a fan of the emissions on these trucks because it will kill a turbo/engine.
This is what happens when the emission stuff gets out of control.