Fuel Gauge is getting worse

Our 2008 Prius has always had an issue indicating we need to add fuel but it has never takes what we assume is a full tank of gas. The dealer says there is no problem with our car and so did nothing while it was under warranty. I never recall ever putting more than 8 gallons in it, even when new.

Now when it indicates one or two bars it only takes maybe 5 gallons. Recently, when we drive into town beginning with three or four bars, after maybe 12 miles the fuel gauge beeps and shows a blinking one bar... after 12 miles. Today it happened again, and the supposedly on-reserve tank (with its blinking one light) would only accept 4.1 gallons after 168 miles on that tank.

Does anyone know what the problem could be? It is ridiculous to have a car with this potential range yet we ALWAYS have to fill up under 200 miles as we don't know which gauge to believe, the fuel gauge or the total miles driven since the last reset. I would feel pretty silly having the car shut down because the blinking light was either accurate or some internal electronic switch used its input to shut things down.

And to make matters worse, many gas pump nozzles shut off almost immediately when I try to put gas in the car, causing me to have to go to another gas station.

Very frustrating. Thanks for any ideas.