Apparently it sporadically happens to various lucky users after all firmware updates including the latest to 4.3!! Though the link references problems after a 2013 update, it explains why the wrong setting "Global Network" sucks the life out of your battery and your signal switches from 3G to 4G or none at all!
Apparently, my settings had never been altered until this last update, almost 2 months later and I've had 4G constantly since I changed my settings!
Verizon & other carriers, I think you need to train your folks on this SIMPLE EASY to FIX issue instead of ???????!!!!!!!!!!!!