What cause a 92 Nissan bluebird car to lose power up hill in high speed 4 or 5 gear?
Consider: it takes more energy to start moving something from
rest that it is to keep something in motion once it is already
moving.
The reason that a vehicle will lose power while climbing in a
higher gear is the same reason that it is very difficult to move
from a stop while in a high gear. Those gears are designed for
keeping higher speeds constant, and, as such, are not designed for
increasing power at the wheels. Lower gears are smaller in order to
provide more power to the wheels when it's needed most.