You have a slight arch in your upper back i would try to work out. Try retracting your shoulders slightly and without cranking the head back just look up slightly instead of just forward.
As far as your heavy lifts i see your upper body is a little slow to the lower body. Your hips lock out and then you still finishing the lift kinda like a romanian. in your speed lifts you can see your hips and shoulders lock out almost simultaneously. Thats how the heavy ones should finish too. Lighten up the weight some if you can't hit that lock out good and then build it back up. Just don't wanna see you strain somethin in your back.
Looking good my friend and strong as hell keep hard at it!!