I would suspect that the vans factory tune isn't designed to take advantage of E85 for a performance improvement. I base this off of the statement that there was only a 2 mpg decrease in mileage as compared to gasoline. That's not much increase in fuel volume. My experience with fuels is that when the same engine is set up for alcohol based fuels we were feeding the motor nearly 1/3 more fuel volume vs gas at the same altitude density. And of course a lot of other changes were needed as well, timing advance, cam phasing, etc. This would translate out from say 15 mpg down to 10 mpg or worse. Plus the fuel system was designed to supply the much larger performance quantity of fuel in anticipation that we were going to use different fuels. Using E85 or M100 methanol would produce a lot more power than pump gas when done correctly. Your van dose all these things automatically after it determines the ethanol content but I have a feeling that as a highway vehicle it still leans toward mileage vs performance even though it "can" run on E85 and as mentioned the ethanol content can vary.
Here is a cool introduction to tuning with ethanol for performance. It's leaning towards turbo powered cars but the physics are the same.
Knowledge Boost: Ethanol Explained - Speedhunters