Crossing lines

It seems that I need to keep an eye on myself at work as it has come to light that I come across as pushy or even disrespectful.
Neither of those descriptions have come exactly from above me, they are more what I understand of being told I can `rub people the wrong way'. Perhaps I do. The way I look at it is that I have a high degree of care about what I do and it appears to me that others I work with don't.
So when I am asked to pick up the slack for others who should really know how to do their own jobs within the time constraints I can get a bit testy, or short in my replies.
This is something of a flaw, I realise, though I don't think it is completely unwarranted to be frustrated by having to do your own job and cover for others.
I might have crossed a line a bit too in a post-work discussion which centred on where I wanted to head within my job. Generally I am quite tactful but when I get frustrated or riled up I can be pretty direct and I was very direct when I was getting across what I wanted for the future.
In short, I said in no uncertain terms that I want someone else's job within my department. This is not a surprise to the person in charge, who has in fact told me in the past that I would move in that direction one day.
Up until recently I was happy to sit back and just work away. Now I have decided it is time to start putting the pressure on. I'm not saying I want to be elevated into a new role tomorrow but it is good to have direction and a goal.
Now I just have to work on my diplomacy skills.