for one, You are creating a slightly false low by topping off twice.
In actuallity, you should:
Use the exact same pump every time (not always a viable option)
Basically, by topping off at all, and being at different pumps, that changes things. Each station, and each pump (for that matter) is triggered at different rates, so topping off at ONE pump twice may allow a quarter gallon in. Others, an 1/8th, or more than a 1/4.
Always fill the exact way (until it shuts off the first time, etc) By topping off the the "nearest dollar" or "twice" (as you do) you are adding more fuel than you ACTUALLY consumed. You then do the math and are dividing those miles by MORE fuel than you originally clicked off at.
Other than math, or topping off:
check your fuel filter... air filter (clean if open air, or replace if stock), plugs/wires, and MAF cleanliness.
Ray
