Hi Stone Cold II,
Select speed that you want select attitude that you want and it will hold it fact.
You are simply using autothrust to try to control speed.
Most of us will climb using a constant climb power setting. A Boeing can be trimmed for speed - an Airbus can NOT. Airbus will hold a constant pitch attitude and the stab will be autotrimmed to follow the subsequent speed changes. It is completely different in longitudinal speed stability - just as the crew of AF 447 discovered.