Default [Q] s4 problem

hi guys. I have a major problem with KitKat. when I press the power button to "sleep" the phone, it takes .1 seconds to fade out to black. in jelly bean it just shut off. I want to know how to make it just shut off or how to downgrade back to jellybean. I know this is a stupid thing to do but i have a good reason to want to downgrade just because of this. If anyone doesn't know what I'm talking about, go go the home screen and press the sleep/power button. now call someone and while the phone call is going on press it. In the phone app the screen shuts off immedietly, and normally it doesn't. I know if my phone were footed it could be possible but I can't find a single f-ing root method for it anywhere. I have an att s4 i337 running KitKat.