2000 Jimmy/Envoy Fuel Gauge Problem

86K miles.
Wife's car.
When she fills it up, it reads full.
Then, it will read wherever it wants.
We just left a store and it read 3/4. 2 miles later pulling into our driveway it read 1/2.
Any recalls or anyone else have this problem and know the "fix"??
TIA
jonny
8-)