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But I find it weird that your inner pages were all PR2 while your main page was PR4. Usually the inner pages take one step down, not two.
However, it may be possible that your website was a very low PR4, on the cusp of a 3.
You can check how close to the border you are by reviewing your Google Directory category (if you are in one), and check the PR of the site directly below you. If it or another one below it is a PR3, then you're probably on the cusp of a PR3.