Is it ever possible to do something we don't want to do? If I think/feel that I prefer not to do something but I do it anyway aren't I really just "wanting" not to face the consequences of not doing it more than wanting to do something different? A really simple example could just be preferring to watch the baseball game rather than driving to the airport to pick up my in-laws. If I suck it up and go to the airport and skip the game aren't I really "wanting" to not deal with the consequences of stranding them at the airport more than "wanting" to watch the game?
It seems to me that there are many layers of meaning to your question: are we free to be moral? Is altruism possible? Can I shape my desires or am I just kidding myself?! In a sense you are in a pretty pickle here, because if I understand you correctly, you can neither prove nor disprove the nature of your choices. Psychological egoism asserts that all actions are done out of self-interest - and any attempt to deny this is simply not acknowledging that your wants might include pleasing your in-laws by picking them up. As a description of our human state, I find this to be a poor account of the complexity of our moral lives. As a theory, it is not open to revision or willing to entertain counter-factual evidence, so it is not even a great theory. Desire is so complex and the human heart so mysterious, I'm not sure we gain much by reducing every action to one (selfish) motive. Perhaps I'm going against Ockham's razor here, but the simplest answer, even if correct, doesn't get me to the airport!