Tuning can definitely help with efficiency, but most of that will depend on how you drive.

Pre-13 trucks don't have a great reputation for efficiency, but you can do okay if you take it easy.

My 12 is still stock, for now, and I can average 14-16 mpg with about 50/50 city/highway driving if I drive normally.

The Lie-O-Meter shows about the same, within <1mpg, hand calc'd too which has pretty much always been the case for me despite the inaccuracy lots of other guys talk about.

Not great, but not terrible for a big truck all things considered and its better than the Grand Cherokee SRT I traded in for it LOL.

Of course if I lay into it the mpg's will plummet quickly, but I do my best to drive easy.

I anticipate my emissions equipment falling off somewhere soon and I would imagine that will help a fair amount given I don't race my truck around.

I have read that the newer SCR equipped trucks do much better in the fuel mileage department, which is disappointing for me because I would love for my emissions equipment to survive and utilize some emissions compliant tunes, but for fuel mileage and longevity's sake I think its for the best for my truck.