I've been thinking about this aspect of my personality too.
Can I offer you a little of my own observations and some prompting questions that may be helpful?
Feel free to keep the answers to yourself, or to share them.
I might lean towards the passive end of things, but certainly have been passive aggressive at times. My mom is generally passive, but does things like tease, avoid conflict, and project. I think I might have adopted passively agressive behaviors as an adaptation to living with her. If I was too aggressive for her, I seemed to cause her to withdraw. So I learned to manipulate, rather than be direct.
Why do you think you adopted passive aggressive behaviours?
Can you describe a behaviour of yours that you recognize as passive aggressive?
What is the opposite of passive aggressive?
I've been thinking that some form of assertiveness training could help in this realm.