I had all kinds of issues with this update. So just wanted to share my experience. Downloaded the update via OTA had serious problems with battery life as well as lag and other odd crazy stuff. I wiped the cache partition several time to no avail . Then I did a factory reset with backup options . still had issues then a factory reset without backup option. Still problems . Finally I used KIES it showed I had the current version but I clicked ok Update firmware anyway and sure enough it reloaded the update via KIES . I then updated everything in the play store. Once that was done then I started re downloading all my apps from playstore instead of using the backup file on kies. This Fixed all my problems and everything is running perfect battery life is better than kitkat and phone is much faster. So there's my story maybe it will help someone.
For those that have a computer ,Have done this on 4 Different GS5 phones and so far it has fix all of them..steps again are Wipe cache partiton> factory reset >apply Firmware update with latest version of KIES> Then complete( ALL) available playstore software updates, then reinstall any 3rd party apps. From what I have seen if you try to reinstall your applications from the backup file in KIES then the problem will return. Not sure why maybe Kies installs the update in a different fashion than OTA or maybe its an app thats not working well with 5.0. But I reinstalled everything from my backup file except applications.