I get 13.9 MPG with my 572 EFI HEMI.
But I had to do some special EFI tuning to do it.

Running very lean at low load conditions.
Lots of spark advance at low loads.
Shut off all the injectors on an decel.
Hold back on the acell fuel (pump shot) unless you mean it.

I run 91 octane, push button 727 trans and 3.70 rear gear.