Phil Needham's assessment is precisely what I had concluded before I read his post.  Spot-on evaluation, Phil. 

More frame weight is definitely needed for sod.  Cutting thru live roots takes a lot of down-pressure, which in turn requires a lot of frame weight.  I wouldn't be afraid of putting 30+ suitcase weights on that drill to get it to work right.  (Actually, I carried that much weight on my own drills when it was needed.)