If you have to ask, you don't want to know
I get 9-11 city in mine, 17-19 freeway. 13-16 avg. Depends how I drive (if like Dear Ol' Dad or a jackass). Seems to me the 2nd gear start combined with the precat and huge main cat are the reasons for the poor economy of the M117 it's not able to breathe easily and struggles to move from a dead stop.
Some time I'll toss in my regular M117 dual manifolds and the first gear box, just too many other projects to deal with now.