I'm still pretty bad on D too. I'm learning that's it more about anticipation, similar to real life. You get caught leaning or reaching and your gonna get beat. Players aren't able to just recover and jump back in front of you like in past years.
One thing I am still seeing is CPU players getting stuck while trying to run plays and whoever has the ball just stands there. I wonder if upping the offensive awareness slider would help at all with that.