I suggest u to using fw 2.1 bb67 global generic, coz this problem happening to me too. Its work for me. Now im using 2.1 bb 67 on stock ROM.
After flash fw 2.1 bb 67, install no-frill and set cpu max to 768mhz to keep your cpu and battery not to hot.
But your device maybe still got random reboot if your cpu work to hard, like playing game.
Please remember, keep your cpu to not work hard and battery not become heat.
Custom rom/kernel dosent help for me. Unlock/lock bootloader still dosent solve my problem, just downgrade and kept cpu+battery not too hot.
Its looks hapening because some parts,maybe cpu or signal chip getting weaks.
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