I would suggest getting AVG Anti-Virus from AVG Mobilation. I would also suggest performing a hard-reset on your phone (returning to factory settings) as sometimes when you upgrade the OS to newer versions it causes issues with the phone on a whole. I would fully suggest using ODIN and flashing a fresh brand new ROM onto the device as that usually fixes almost EVERY single issue with the device in question. I did it with my Samsung Galaxy S2 Epic 4G Touch and it fixed all my issues after upgrading from Gingerbread to Ice Cream Sandwhich.
I would also try going into your phones recovery ROM (google how to do it with your device) and clearing your cache. That can also fix many issues caused by devices.
Last but not least I would suggest getting an app called Juice Defender as that helps to preserve battery life and also seems to stabilize the phone's operation. I don't know why but my phone always runs better when I have Juice Defender installed.
Hopefully some of this helps you out.