If
you are holding a constant pitch angle it means the angle between the
longitudinal axis and the horizontal is constant. (constant
nose position) If you are at max thrust at MSL, the thrust will decrease as you
climb, so will have to increase the angle of attack to hold the nose position
constant. That means the IAS will decrease. The gamma angle is the flight path
inclination and that will decrease as well.
At somepoint the thrust will be so low that you can
only maintain S&L at the stalling angle of attack, so gamma will be zero
and angle of attack and pitch angle will be the same.