If you're going to exchange it anyways, why not Odin back to a 100% completely stock 4.3 TW and see if you are having those issues. Just remember, it's better to figure this out and learn from it just in case this ends up happening to you again. See, because if you go Odin back to 4.3 TW, and you still have this issue, then you can confirm it is a hardware issue. But if you Odin back to 4.3 and you don't have those issues, then you know something in your ROM or services was modified or corrupt. My suggestion, go back to stock and test it out.