Squats looked good, form was right there. Keep working the sumos, they'll build your hips, but do what Sean said, hips high and close. Watch Sean, Rodja, NomZ, or any bigtime sumo puller and watch how far forward their hips go. It's like smack between their knees and their knees are behind the bar. Here's my favorite vid to watch for sumo, I've linked it several times before. Shoulders slam back, he spreads the floor to get the thing moving, locks his knees violently, and then leans back SLIGHTLY to finish the lift.
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