Didn't you say you don't have 4G service in your area? I assumed that since you can only obtain a 3G signal, that leaving the phone in "CDMA/LTE" mode would cause the phone to constantly try to connect to 4G, thus draining more battery. By staying in CDMA-only the phone quits trying to find a 4G (LTE) signal, which shouldn't be an issue since you said you have no good 4G service anyway.
Every month or so, you can turn your setting back to "CDMA/LTE" mode for 10 minutes to see if you can grab a 4G signal. Also, you can check somewhere on the verizonwireless website to see if the LTE network is available in your area (you can type in a specific address to see if it is available). Until that happens, just keep the phone in CDMA-only mode.
Same thing with the WiFi. Are you leaving the phone's WiFi radio on when you leave the house? If so, the phone is constantly searching for a wireless router to connect to when you move away from your home's connection. And since there are a lot of wireless routers out there, as you walk the dogs or drive around town, the phone will be constantly exposed to different routers and try to read the output from them, which takes battery power.