I have a fairly steep quarter mile hill on my commute that I would ride up five days a week and for over a year I was always out of breath when I got to the top. This past winter I mashed my way up this hill on a single speed bike for three months. When I went back to the geared bike I was able to sit and spin up the hill and now it is no problem (unless I am really tired). I know because I ride six days a week I generally don't ride hard enough to push my body to get stronger and I don't ride slow enough to recover. Maybe you could look at the hill as a goal and train to ride up it comfortably. Do intervals and ride fast sometimes to reach the goal. Also, +1 on the low gear and spin technique.