ROMs Problems with Viper S on HTC Sensation


So here is the whole story:
I haven't got a lot of experience in Android roms so any help would be appreciated.
I flashed Team Venoms Viper S sense 5 on my htc sensation using 4ext recovery.
I made a full wipe of my phone, installed the rom and overclocked the CPU to 594khz minimum frequency and 1512khz maximum. The ROM installed perfectly and runs smooth as butter. The problem is that when i run something that requires more power my phone shuts down or reboots. After a reboot a fully charged battery shows only for example 3 percents charged and after i take out the battery and put it back in it again shows a 70-80 % charged. I was told that i should calibrate my battery. I did that, but i still have the same problem with shutting down.

Also i tried restoring the CPU speed to 1200 khz but the problem persists