Can you imagine telling an officer - "I know I took off fast, officer and I didn't mean to chirp my tires. But it's really the only way to get good gas mileage in this thing!"I've noticed this too! Accelerate to speed very lightly? Poor gas mileage. Get up to speed quickly and stay there? Much better!
Makes sense though. The instant fuel economy while accelerating is like 3-5 mpg. It's better to get it over with quickly, than to drag it out.