Hi Ron,
The first thing to ask is when you were seeing your website ranking around 4th how did you do this? Did you use a ranking tool or your browser. The reason I ask is that when using a browser your search results can be personalized to you. So if you often go to your website then you may see it for a keyword search when really it isn't placed there. To be sure exactly where you rank use a non-personalized search or a ranking tool like the one on SEOMoz.
Second, it doesn't look like you are doing anything odd on-site (i.e. no black-hat seo tactics) so that's good. And, your backlinks are low so not sure if that would be the case but you need to have a look at Google Webmaster Tools to confirm.
Thirdly, a drop in rankings could be due to competition. If your competitors are actively optimizing their website and building quality links and you aren't then they can knock you off the rankings.
Hope that helps some.
Davinia