In a geared vehicle,won't there be any loss of energy in other gears other than top gear?

Answer 1

There is always a loss of energy. It is the LAW.
The question is how much?
The loss of energy is seen in its MPG rating.
The greatest amount of energy is required to start a load moving so a low gear is used. As speed increases the amount of energy required to change velocity decreases until the resistance of the air becomes that of a liquid.
I ramble. An automatic transmission is less efficient then a manual.

Answer 2

Not in my opinion. There will be a loss of MPG's but when you are in the lower gears, you are using them to accelerate the car and the gears will give you the torque multiplication that is required to get the car going. So you are not losing energy, you are just using a different power range.

good luck.