If you can, try to load your hams at the top of the lunge the same as you would a squat (butt out, big air, stomach out, etc.) That might help. I'm not really sure. I would try it, but I'm kind of MIA.
You have 170 in the bag. Did you attempt it again? When I pull sumo, if I can get it to budge a millimeter, then I can pull it. You got it moving okay....I bet you could pull it.