Hi M Hardin, what you're describing is called truss uplift and it is quite normal/common. The March issue of Popular Mechanics has an article (Journal section) describing this and what steps need to be taken. You might want to go out and buy this issue so that you have a "hands on" reference. However, to sum up the article what you need to do is install crown moulding nailing into the ceiling and not into the wall. This will allow the moulding to slide up/down with the temperature changes and hides the gaps. Hope this helps, and good luck!