gas gauge problem on 2007 Buick Rainier

gas gauge drops off to empty after only four or five gallons are used. when you fill it up it reads full again until 4 or 5 gallons are used. it started doing this at about 51,000 miles.

Asked by for the 2007 Buick Rainier
Most likely your sending unit is going out, to correct this you will probably be replacing the fuel pump assembly.