Definition of self-righteous: having or characterized by a certainty, especially an unfounded one, that one is totally correct or morally superior.
I guess it's perception, but from my perspective you absolutely are being self-righteous, especially in the words you used to refute.
I actually stand corrected on the legality of passing on the right. So you are correct that you are under no legal, and hard to argue morality unless we first agree on the basis of morals. As a Christian I would say that staying in a lane because you are mad at the jerk coming up behind you is not doing to others as you would have done to you.
This really is more of an issue of the person that is going below, or at the speed limit while flow of traffic is dictating a faster pace. So maybe you aren't the target of road rage, but road rage is crazy nowadays, and it comes from all of doing what is "best" for numero uno. And what you are doing is just adding to the rage. As I'm sure I do.
I think this is all summed up by the late great George Carlin:
“Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac?”