yep, I had the same problem so I changed my modem back to EL29 and the problem was gone, in the app betterbatterystats it didn't show my phone constantly searching for signal either and preventing it from entering deep sleep.
I'm on a custom Rom. But you can just flash a custom recovery with Odin and flash any modem you want from there, or just use Odin to flash a different modem. Since you even asked, I am assuming you are not rooted?
You can just flash your modem using Odin. There's no issues at all doing it, as any modem version is compatible with any software base, even across different OS versions. I happen to actually be running the EL29 modem right now.
Fyi having a non-current modem on your phone will cause future OTA update installations to fail, so you'd need to flash back to the current modem before you take an OTA update.
If you're interested in flashing your modem let me know and I'll reply back with instructions once I can get to a PC so I can link some files.