Google SERP is now Unpredictable

I don’t know if I am the only one experiencing this but it seems that Google now a days seems unpredictable, Some of the keywords is like dancing, One day it is in the first page the next day it is on the 10th page then goes back again to 1st and so on and so forth.
Do you experience the same ? Is it because Google will now introduce a new search engine algorithm to match bing ? There has been some reviews in the net that shows bing is better that Google. So will this continue or they are just experiencing a system glitch ?
Anyway this happen to my main Technology Blog many times, but before I always do excessive link building. But I don’t know what happened now, I don’t know if I did something wrong because I have seen that my Google Webmaster’s Tool reporting that there is something wrong with my Sitemap. It is reporting 403 Error. [ Btw it is now fixed ] even if I can access it manually.
I just fixed and hope that it will all be fine.
I think I need to have some incoming links since I have not received incoming links for the past months and I rarely do bookmarking in social media sites.
Anyway I hope all will be fine in the next days.