You do not need a whole bunch of backlinks to get a pr 6 or even a 5. I own 2 website that have these pr's with very little backlinks. http://www.fapeonline.org (PR 6 with 19 backlinks) http://www.onlinemarketingadvisors.com (PR 5 with 17 backlinks) It is not about how many links you have, but the overall quality of those links is what counts.
Google's backlink checker has errors for sure...it says my site has only 2 backlinks when it has well over 20