I'm no expert, but if you've tried a variety of bullets, you should have found a suitable load by now.
I have a Remmy SPS which shoots 100 gn Privi's tighter than that, your Sako is of far better quality.
As someone said before, let someone else try the rifle for you, just to put your mind at rest.
If that doesn't work, have a serious word with the person you bought it from.