This has got to be THE most worn-out subject on this forum but here we go:
The only thing that will give an increase in altitude (get back on glide slope if below) without a reduction in airspeed is power. You need to add more potential energy to the aircraft. Hence power controls altitude and ROC/ROD. Airspeed is controlled by AoA (CL(pitch control)); you will not find a single aerodynamics text book that states otherwise.
If you have trimed the a/c properly, say, in a descent, and add power, you will INITIALLY accelerate somewhat. But the AoA (CL), for which the a/c is trimmed, wants to remain constant (in the trimmed position) ans as the lift increases you will either slow the descent or enter a climb.
For every AoA there is a corresponding CL, which in turns equals a certain airspeed. Pitch = airspeed. Now, if anyone can find an aerodynamics expert who seems to think otherwise, please let me now. But you won't.