well, as far as i know, rocksmith actually does set the level of a new(never-played) song based on your performance in other songs but this just can't be the case for my downloaded cdlc's. right now i play my songs at 20%, after some practice up to 30 or 40... But every cdlc looks and feels like >90% and is simply undoable for a beginner like i am. I guess, setting the difficulty by using the riff repeater is the only way to solve this. Set it to 0 or whatever suits me, then start to play and practice and let rocksmith do its job again ;)