Default I9300 ON 4.3 Official - Slow, Laggy and Screen Flicker when swiping

Hi guys ive got a Samsung s3 which is on 4.3 official stock rom, however im having some problems. Firstly is the problem of lagging, for example i could be using the browser and when i go back to the home screen there is nothing there and it takes a few seconds for all the icons to load back.

Second problem which is intermittent and usually goes away when i reboot the phone is when swiping through the homescreen i get these weird screen flickers (Not sure if screen flicker is the right word) but basically i can see my other app icons in the background which become enlarged. I have included some picures to better explain. Do you think this is a hardware or software fault and what should i do?

Any helps appreciated, Thanks.
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