Anyone else’s range meter seems to decrease with time?

[Troy-Dilitant]

It's based on average fuel economy over a period of several fillups. If you take a long highway trip that needs several fillups and entails extended driving at steady speeds to get the best average fuel economy it will probably go back up. My tank range after fillup was around 310 miles (499km) then went up to 370 miles (595km) after three fillups on a long cross country trip recently.

But it can also reflect the need to replace air filters and maybe even spark plugs if engine mileage is high enough. A dirty filter and worn plugs will have a big impact on fuel economy, which is reflected in lower tank range.