OK PR but terrible Serps

Crosslinking and virtual server IP issue

[NZ_Mark]

I have 4 domains pointing to the same pages, each domain is a regional domain with the appropriate regional content (title, meta data and page content) displaying for each domain. There is some crosslinking and they are all on the same IP (virtual hosting package).

I have learned through WW archives that this is not such a great thing to do as the page content is similar although easily outside the 10% threshold. Incoming links are good at over 100. What I dont understand is why do they all have PR of 5 but with absolutely awful SERPS.

Previously I had one domain and I had it top 5 for many KW and now its the shape of a pear. If I was banned the PR would be grey or 0.

Any thoughts?