Question: On fuel economy

[Sempercoasty]

I know most are thinking "who cares about fuel economy, you drive a Vette!" Ever since I bought my '11 GS a couple years ago, when I fill her up the "range" on the DIC has always read around 411 miles till empty. Well yesterday I filled her up and the range on the DIC read only 248!
What happened to my other 160 miles?! I have not changed anything on the car between the two fill ups except what the dealership did by replacing the RDLCM mentioned in my other thread. But I would not think that would change my MPG.
The tire pressures are exactly where they need to be and my K&N air filter is clean. The car has just over 50k miles (yes, I do drive my car). I'm wondering if it is time to change spark plugs or fuel filter or something? Any thoughts? Or should I just wait till next fill up and see what happens? Thanks!

 

[Tony1Leo]

The mileage it shows to empty is based on your driving habits before you fill up. So if you were driving conservatively on the freeway for the last 25 miles or so, it will show higher miles to empty because it's going to assume you are still driving that way. If you have been driving a lot of stop and go or hitting it hard a lot before filling up, it's going to show lower miles to empty. So it's basically based on your average mpg for the 25 miles or so before you filled up.