I always had (and still have) trouble sight-reading because I play by ear. Back in the days when I was a kiddy and still having piano lessons, when I given a new song I go and program it into my TI 99/4a (the speed at which I could type in a CALL SOUND statement...) so I could figure out what it sounds like.
Once I started doing that it was heaps easier to learn the songs I had to play. Not at all helpful WRT my learning how to sight-read, though...