I seem to run between 10 and 14 mpg. In my case, tire pressure can play a significant role as there is a noticeable difference between 65 and 75psi. Wind direction and wind speed are the largest variables I have to deal with, especially at highway speeds. If the wind is in my general direction and I'm keeping the speed no more than 60MPH, I can usually expect between 12-14mpg. If I'm going into the wind at 65+, 10mpg is all I can manage. I've never had better than 14mpg, even when I was running stock tires and far less weight.
2010 E350 RB with the V10
5Star 87 Tow and 87 Performance Tunes now - need to calculate MPG again.
UJOR 6" Lift with 35's and 4.10 gear ratio.
Not towing anything
Probably weigh about 7,500 lbs right now.
Probably about 10mpg around town if I'm conservative
12-13 on the open freeway but only if I keep it just 70mph and the wind is with me.
9-11 on the open freeway if I'm above 70mph or I'm against the wind.
9-10 going up and down the front range here in CO.
E350 PSD UJOR 4" 285x75x16 BFG's at 65-68lbs, DP tuner, diamond eye exhaust, 8000 lbs., roof rack with 2.5 feet of boards stacked on top. During my last trip I averaged 14.5, from SLC - Whistler and back, Oregon Coast in between, 40 miles of off-roading. I get 15.0 on my 15 mile commute to work in mountainous terrain, sans boards on top.
So are you folks happy with the kind of mpgs you get? Seems like only Sprinters can beat my 1989 vehicle's fuel efficiency. Of course I realize most of your vehicles are heavier than my little van and have more power and may have 4x4 capacity and other features, but still, you'd think in all these years, the auto manufacturing industry could come up with more fuel efficient engines than they have on offer.