Do you touch your chest to the floor when you do pushups? If not you're only doing partials, which are a lot easier.
Unfortunately I can only go down until my stomach touches :-)
I wonder if this could be a shoulder imbalance rather than chest/back? I really have been careful to balance chest & back, but for a long time the only shoulder work I did was military press, which mostly hits the front delts. Maybe my front delts are way stronger than my rears and that impacts these exercises?