TAS increases with altitude for a given power setting due to less
aerodynamic drag at higher altitudes. It does not take more power to go
the
same speed at higher altitudes

It doesn't take more power to go the same TAS, but it does take more power
to go the same IAS.


The way most people fly, which is well above best L/D, the same TAS will
require less power with increasing altitude.

Peter