My Greg Bennett Edition Bass - I have had it re-strung, completely re-fretted and everything fine. But now I have a very slight bow in the neck right around the 9th-15th, and cannot seem to keep it in tune now. I have GHS Boomers on it and they are relatively new. I am just at a point where I do not want to get rid of it, but do not know what to do. Can you help me?