Just picked up about 3 weeks ago and has about 1500 miles (will post pictures soon) but when I filled up the first few times the mileage range that I would get was about 500-525 range, and then when I filled up today (with a full tank) the range read out was only 445. Why the sudden drop off? I know that the gauge is not accurate and that it is based off of current driving conditions (i.e. how fast/slow you go) but why the drop?

Any suggestions?