Most, well alot of musicians who are good at learning a song right off the back pick up the bass line first. Alot of times at my church, my m.o.m. will just throw a song out and we'll have to learn it right there. Listen to the whole song first. Then decipher the bass line. If you've been playing for a while and are pretty decent, most of the time you can tell wat chord will be played with what bass such as usually in the key of Eb, there will be an Eb major chord on a C bass, usually. It will come easy if you just keep playing different songs and learning the pattern. And I kno how it is because I was the same way were I could read but not play by ear. Um, also, i'm a second keyboardist as well, and because the other keyboardist plays acoustic piano, im forced to find some other instrument. Usually horns, or strings or something. If you've got a nice board, it should come easy.