Why gas gauge reading is inaccurate

What is your question?

When I put gas in my truck,, it reads inaccurate when I turn key on, it reads less.and reads more when I turn key off.

What makes this problem better or worse?

It's better when I add gas. But run out when I'm driving. With no leaks.

How long has your 1999 Chevrolet Tahoe had this problem?

For about two weeks. Fuel pump is less than a yr old. It's an AC Delco.