Both the Global RUU (4.3.605.12) and the stock OTA update (3.14.605.12) use the same Android 4.0.3 as a base (there is no 4.0.2 for the Rez, or any other ICS base), the only real difference is the modems and additional settings to go with the additional modes officially supported, and bug fixes. You should be able to just flash back the "official" OTA firmware, although I haven't tried it... generally, hboot will not allow you to go backwards in revisions unless you are S-OFF (a procedure not to be taken lightly), so to be honest it's a 50/50 chance it will work if you are stock. If you want to go all the way back to Gingerbread firmware, you are required to go S-OFF to do that and I would not recommend doing that for a stock GB ROM unless it is only for troubleshooting or temporary use.
Most people find the Global Mode RUU is more stable and battery life is improved... The fact that you are having other issues as well makes me wonder if you got a "dirty" flash and something didn't take correctly, but you didn't give a lot of details as to the problem.
If it was me, then I would reflash the RUU, twice! Then do a hard factory reset from hboot, and setup the device... then install only absolutely essential applications and see how it goes for a while and see if the situation improves, then slowly start adding other apps to see when it breaks.
That being said, the Rezound is not known for it's battery life... getting 2-3 hours of screen time on standard battery with excellent signal is normal, if your signal strength is marginal or poor then battery life with suffer significantly irregardless of the ROM or version used.