Are you sure?

Positive.

Here's backup:-

From http://www.av8n.com/how/htm/power.ht...power-altitude

"Let's compare high-altitude flight with low-altitude flight at the same
angle of attack. Assume the weight of the airplane remains the same. Then we
can make a wonderful chain of deductions.

At the higher altitude:
a.. the lift is the same (since lift equals weight)
b.. the lift-to-drag ratio is the same (since it depends on angle of
attack)
c.. the drag is the same (calculated from the previous two items)
d.. the thrust is the same (since thrust equals drag)
e.. the indicated airspeed is the same (to produce the same lift at the
same angle of attack)
f.. the true airspeed is greater (because density is lower)
g.. the power required is greater (since power equals drag times TAS)
The last step is tricky. Whereas most of the aerodynamic quantitites of
interest to pilots are based on CAS, the power-per-thrust relationship
depends on TAS, not CAS.

This means that any aircraft requires more power to maintain a given CAS at
altitude. This applies to propellers, jets, and rockets equally."