The first 500 miles on my truck it said 9.5 MPG, but that was mainly city and short trips with more than a few hills during stop and go.
I just got back from a 500 mile round trip with my 2500 megacab Gasser and I averaged 13 MPG with a little city driving mixed in. My truck only has 1100 miles on the motor so I expect it to get a little better. I was going 80 on the freeway, b/c the ride is a little better. Road was fairly flat(NortherN ND) and my tank had 91 octane with no ethynol. 3.73 gears.
Since my trip I have reset a few times and it seems going 60 I could possibly get 17mpg, and also possibly rear ended
I too did not need a Cummings and am happy with my gasser!