A couple of points:
For one thing, i had a 96 chrysler van (same body style) that would randomly add mileage to the odometer! For a while i thought the van was AVERAGING 25mpg. It was not.
Second thing: I have put a lot of miles on a 94 3.8L Town and Country (different body style, smaller frontal area but worse aero, probably ~200lbs lighter) and it actually does surprisingly well on the highway when driven kindly (no hypermiling at all). I have been able to do 26mpg sustained on the highway with that van, bone stock.
So, i do not think this is beyond the realm of possibility. But i do think it is unlikely. If you can back it up with future measurements, well, that would be cool.
