It's been awhile there may have been something about rep only increasing when up voted by someone with a better rep than you so people couldn't use their bots to vote back and forth and drive their rep up.
As long as you have people higher rep than you up voting you your rep should increase.
I think that is actually why it gets slower because as your rep gets higher it is less likely the people up voting you will have a higher reputation than you do.
RE: You cannot take away from the author that which does not belong to the author.