I havn't read the whole topic so i don't know if this has been mentioned but:
-when you jump (1 legged) point your arms and fingers down, or the free arm and fingers if dunking, this helps

I was watching a video on youtube and this is what it said, for more info just search for a guy by the name "stretchexpert" on youtube.

Another thing is,,,, this is not so important but, I am right handed but used to jump off my right leg (using my left hand to grab rim), but i couldnt palm the ball so i used my right hand, meaning i had to jump off my left leg. I couldnt do this at all.

But i kept practicing and now i can jump alot higher off my left leg than my right.

The point is KEEP PRACTICING AND YOU WILL MAKE PROGRESS!!!!!