John P. Yeah, whistling is good. But if you really do have a disconnection between your brain and your vocal chords, you probably won't be a very good whistler either. However, being able to sing the tune in your head is more than adequate.

The thing with learning to learn tunes by ear though is the same as anything else. It's really just practice. The more you do it, the easier it gets. I suspect you are slow at it because you haven't practiced it much. Simple as that.

(by the way, we are not saying the same thing. Don advises beginners to learn to read. I'm specifically advising beginners in a genre new to them - especially if they can already read, even a little bit - not to read. For the reasons above)