[Q] Help a newbie out

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http://forum.xda-developers.com – Evenin' xda! I'm the proud owner of a non-rooted SGSA and I am having a couple issues I couldn't get my head around so I was hoping that you guys could give me a hand. My phone's csc was MTL (not my country's csc) and since I couldn't find any JB version made especially for this csc I flashed one released for my country (COA). It ran really smooth for a couple of weeks but every once in a while my systemUI keeps freezing ,or I get some really annoying lag spikes while performing easy tasks like messaging through the stock app or browsing my contact list. Now, should I flash some other (HowTos)