There's a few things I actually like, you don't push onto your front foot when you jab, that's very good. But you do when you throw the uppercut. Right when you turn for the rear uppercut, set your weight back onto the back foot. You should notice a significant difference in how hard it is, and you won't need to straighten your legs and push upward to generate force. And don't lead the uppercut with your head, lead it with a turn of your hips. Keep your chin down and chest up.
In the second video, when you throw the 1-2, you ARE going onto the front foot and straightening your legs, so you're standing up tall. Keep your weight down and knees bent. Your back foot also stays pointed sideways when you throw the cross, it need to turn inward the same way it does when you throw the rear uppercut. Keeping your weight down will also help you with the lead uppercut, because it looks like it feels awkward for you. Bend your knees on that hook to the body as well, otherwise the whole side of your face is exposed and a simple jab will knock you off-balance if you reach down for it.
You also need to keep your elbows tighter to your body. If those elbows are floating out in the air, you're throwing arm/shoulder punches, which are not only not as hard as proper punches, but they make you more vulnerable to injury. The shoulders are weak joints, don't depend on them to hold the force of your bodyweight in motion, that's asking for a torn rotator cuff.
