You are too loose. Tighten your back up from top to bottom. Your knees are sliding too far forward - particularly at the bottom which is costing you elastic rebound out of the bottom. You need to lock out at the top - from the time you unrack to the time you're done, it looks like your knees never lock out. You are shallow, particularly at weight. Get a set of film from the back 45 degree angle. Also, in the first video, what's up with the black things that look like they're projecting up from your hands?