Gas mileage? What gas mileage?!!!

I get around 14-16, if I keep the ol' size 14 out of it. I am running dual Holleys on an Offy intake, it does run a bit on the rich side, plus we have E-10 here. The trans is an SM318/Borg Warner, original type option for that year truck. The diff is also the original. About the only real change from stock is the tires, a 30x9.50x15 Michelin radial LTX MS. I can run around 70 at 2100 rpm with that combo.
I should mention, mine is a 1/2 ton, not a 3/4.