Be careful not to slow down at any point during the pull - as you move into the hips, you're slowing down a bit, probably because you're mentally preparing to accelerate at the hips. Keep the bar moving at least at a constant speed until you initiate the explosion.
Next big thing is keeping the bar closer as you pull under. That handy bar path tracing should show you pretty clearly that it's moving out too much. When you finish your extension, make sure you're getting a good push up with the legs and also actively pushing the bar back against your body with your lats.
Initiate the pull under by pulling the elbows as high as possible and out to the sides while still actively keeping the bar as close to the body as possible.