I';ve been having lots of problems with Yahoo lately..... Seems like ever since there PPC program went full fledged their recking the index....
Yahoo doesn't have a sandbox that I'm aware of. They'll grab your front page and then take forever to display your content pages, and your rankings may fluctuate up and down frequently for no reason. Aside from those factors however, there is no sandbox that I know of. One big factor that seems to make a big difference is not just your on-page optimization, but your anchor text links coming in. Ian
If you still have only 5 backlinks then that could be the reason. Yahoo seems to favor inbound links with keywords in the anchor text and low kw density.