There's a little more to it than that... gap between gears, power-to-weight ratio, and overall drive ratio of the transmission, rear end gears, and tire revolutions per mile all factor into it. Plus there's the engine itself... when you say six cylinders, you could be talking about an old Ford 3.0, or a semi truck engine (they use an inline six engine, typically displacing 13 to 16 liters).
You probably have a 4 cylinder engine (A.K.A. the V4 Engine), V4 engines aren't very powerful, I previously had a V4 and I had the same problem.
When driving uphill, gravity acts against your motion, decreasing your kinetic energy. When driving downhill, gravity acts in the direction of motion, increasing your kinetic energy.
Gravity remains constant regardless of the direction you are driving in. However, the gravitational force may feel stronger when driving uphill due to the incline causing a greater component of gravity to act against the vehicle's motion.
Engine is in need of tuning.
Gravity.
its getting ready to explode. jump out quick
Time for a tune up.
With a forklift, carry the load on the uphill side.
It depends how high you're talking about. If you mean revving all the way to the red line then yes this is bad for the engine. But the rpm shouldn't exceed 4000 rpm. If it is slightly below this then it is fine.
Using a lower gear while driving on steep inclines provides better control over the vehicle, increases engine power, and reduces strain on the brakes. This can help prevent the vehicle from rolling back and improve overall safety while driving uphill.
You're driving an automatic, the car should select the correct gear for you. However some automatics allow the driver to select low gears for use in slow moving traffic for example. If you feel you need more power when driving uphill then select one of the lower gears.
A Ford Ranger may die going uphill due to ignition problems. There could also be a problem with the fuel injection or fuel pump.