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.