GUACAMOLE - what happened to my gas mileage?!?! It got BETTER!!!

Gassed up yesterday (had "30 miles to empty" showing) - 389 miles since my last fillup - and my gas mileage has rocketed from 10-10.5mpg, to 14.5mpg!!! I put a lift, bigger tires, and a Fastman throttlebody on it, and the mileage gets BETTER?!?!

NOTHING added to the tank - I'm still running 89 octane on an 87 octane Superchips tune. I'm still stopping & going @ stop signs every 5' here in the hills of Pittsburgh - my driving habits haven't changed, and neither has my terrain. I'm not complaining, mind you...