Hey Matrix, if you are doing only scrapebox blog commenting and specialy on autoapprove blogs with hundreds of comments on all pages, most of them are no do follow than you will always experience same kind of Google Dance, for few days your site will be in good ranking and then it will push towards to last pages and this will repeat again and again.
So, main thing is that you have to make a good strategy about how to acheive good ranking and how to diversify your backlinks. You have to work on all kind of backlinks from web 2.0 properties, articles, bookmarking, web 2.0 profiles, forum profiles, RSS and then blast your backlinks with scrapebox comments and with xrumer blasts et. etc. and it should be on regular basis for atleast 3-4 months.
If you follow a good strategy your site will stop dancing and you will get some good position may be TOP 5, all depends on your strategy and your competitors.