No the can go faster downhill or uphill
gravity!
Engine is in need of tuning.
Gravity. The car is heavy and doesnt want to move, so you must excelerate to make the car go uphill. If a car is going downhill, the is no need to excelerate because gravity is pulling the car downhill.
check the air intake
Time for a tune up.
Gravity if going uphill. Friction.
The engine works hard and produces a lot more heat than when the car is driven on a leveled road. The car is usually driven slower on the uphill and there isn't as much air cooling the radiator. But the main reason it overheats is that the cooling system is malfunctioning.
Your car is starting to overheat or your thermostat is going out. Get it checked.
If the slope is 'uphill' then the car is going faster
Engine straining Low coolant? Cooling fan not working? Plugged or restricted radiator? Water pump? System airbound? Defective radiator cap?
Electric fan or fan clutch has failed.