i dont think i have that problem. try reflashing

Wipe cache n data. Reflash if necessary

use ure twrp or cwm(refer 1st page for more info).clear cache and dalvik cache.

did you make a clean install? cozim using cm10 as well and my phone is quite smooth for daily use.

i believe everybody will say that it is better to not use any task killer app as android ram management is pretty good itself.

While it might be true, task killer has it benefits too, it stops those apps that cause wake lock. Usually when they say task killer drain more battery it's because certain system app will restart itself even though u force stop it, so the process of restarting takes up more battery power. U can use task killer but make sure those app that u stop aren't restarting itself, like for example Facebook has no exit option so I had to use task monitor to stop it running in the background

yeap you dont need to. it is said that those apps only makes things worse. i don't know how true it is coz i dont use them.