2004 Pontiac Sunfire Gauges

I have a 2004 Pontiac Sunfire that had a small problem with the gas gauge, when I filled the tank full it would go way passed the F and into the speedometer range. Once the fuel would get to about 1/2 a tank it would decrease to the correct amount. Well, I Have since then given the car to my wife she knew of the problem and didn't think anything of it. Well just recently all of the needles are acting incorrectly. The Engine temporature is is always at 260 in the red zone. When she is at a stop light (stopped) she is going 20mph. I think the only thing that isn't messed up is the rpm