Toyota Repair: Tercel 94 gas indicator always full, toyota tercel, gauge readings

Question
I have a Toyota Tercel 94. Its mileage is 76000. As soon as the engine start, its gas indicator points to the maximum position even though the gas tank isn't full. Then after the engine is on for a while (around 2-3 minutes in the morning), the thermometer needle also points to maximum position. However, the car is running well, I tried to drive it around 40 miles  non stop, It is OK. Could you please tell me what's wrong with my car. Does this problem have something to do with the gauge in the fuel tank? A mechanic suggest me to replace the  gas and temperature indicator and speedometer circuit on the dashboard. Do you agree with him?

Thanks

Efta


Answer
Yes, the problem is in the dash not in the fuel tank, the mechanic that recommended this repair seems to know what he's doing, one of the gauges has a voltage regulator in it that can affect the gauge readings of both, and he is probably also recommending replacing the printed circuit board which should fix the problem.