Is it possible that Google is working some kind of FILTER?

stuck at position 85 for 8 weeks for 2 word kw term?

[stringsandbeyond]

Has anyone experienced a google filter which leaves you "stuck" around position 80-100?

We have a clean site and we have really tried many different things. We can't go up in rankings no matter what we do. We have been stuck there for 8 weeks. (We previously were in the top 5 for this keyword)

We have a pr 5 and many backlinks with good anchor text for the 2 word kw term but just can't seem to break out of this filter.

Thanks for any help.
Mike