I used the proper amount of DME, but instead of 4lbs and 3lbs of LME respectively, I used 3.3 of each because that is what my brew store sells them in. I find it hard to believe that a difference of .4 lbs can account for that much of a difference. Maybe part way, then other things like boiling over and an inefficient steep (can those be inefficient?) make up the rest.
In the end, I'm not worried. I'll still make beer, but it would be nice to know why and learn from it.