I am looking for an experienced SEO expert to give me the right advice
to break a filter/penalty that is currently being applied to my site.

the page i am trying to optomize is www.stringsandbeyond.com and the
keyword is "guitar strings"

I have a pr5 for my homepage and i am in the top 3 for allinanchor. Go
rank kw analysis shows that I compare with the top 10 rankings in all
categories for the 2 word kw. I used to be in the top 3 but I was
completely dropped during Florida and then reappeared in March in the
top 3. Then in May and June I was dropped again and slowly went from
800 to 80 over 5 weeks. Now my site is "stuck" or being filtered and I
have been sitting around the 70-85 position for this keyword for 5
weeks.

Can anyone advise me how to break out of this filter? I have tried
changing content. I have changed title. I have changed internal anchor
link text. I have added an outgoing link to an authority. I cannot
figure out what is going on here. 

How can I get passed this filter and back in the top 10?