[Firmware] Upgrade from diff. Regions

My phone came from vietnam and its stock rom is from vietnam when im using the phone on internet 3g etc it doesn't get hot at all..

after upgrading and testing from other Region firmware... my phone gets too hot..

Anyone... whats the difference on different region firmware? except the csc...

cause if its only the csc is different then... United Kingdom gets xxlj4 then other countries should get LJ4 but not ... others get LIH and LJ1

why is that so?