USAF Aerial Gunner, high washout rate?

I had read that Aerial Gunners in the USAF have a high washout rate (3rd highest) for their schooling. Anyone know why? Is it true? What does the schooling consist of? Anyone know if there is a way to tip the scale in my favor for this job? I scored pretty high in my ASVAB (I can do any job with my scores) I have 60 units of college so I'm going in as an E3. Anyone suggest anything else? AF can't guarantee jobs just fields right?