difference in the energy of the ethyl alcohol molecure as compared with the assorted HC molecules which make up the gasoline mixture.
E-85 would produce the "desired" resuts.
Although, emprically, it does "seem" like 10% C2H5OH knocks mileage of my 2001 Silverado down at least 10% as well.
To achieve such a result—as if alcohol has NO thermal energy?—I can only guess your pickup's ECM is a Southern Baptist.