Its simple, just add high PR links(PR5-PR8) and your PR will increase accordingly.
I've been doing High PR3-9 EDU backlinks but it didn't help my site's PR.
You got Pr3-9 links from the actual page/homepage or a new page? How has it been since then? Google doesn't update the public PR every week.
When setting up your site, it is important to add text links on the multiple pages. When using image maps, links for images, or drop down menus, it is important to add text links because the spiders need them to have something to follow. This is important when it comes to the way you rank on the search engine results page
I don't know why no one mentioned this, but it has been discussed and tested before. Multi Language adds on page rank.
Translate your site in another language besides English, maybe your native or so and add a multilanguage option. Just don't use google translate, it wont work.