I am on my second playthrough and I am 1/2 way to level 5. I have not even ventured in to the underdark (on this new run) and I have not...
killed the hag, spider, gith battle, and a few other things above
completed some of the other major battles above ground.
I suppose you could only accommodate this request if EA and the game even supports those higher levels because you can see that stuff already bugs out like, for example, being able to spec in to a wizard with a number of classes.