Follup up / more info
Based on posts on other forums, I tried excluding LTE from my preferred network types, and my battery usage improved dramatically
. If I choose 3G, signal strength is 2-3 bars. 2G gives me 4-5 bars. With LTE I get 0-1 bars - mostly 0. On 2G my battery life is the best I've ever seen
My suspicion is that the sudden change I saw was caused by a change in the way the radio software selects network speed options. It appears that if the preferred network type selected is LTE, the phone now will expend maximum effort continually to connect to LTE, even if there is no useful signal available. Before the change, it's likely that a stronger LTE signal was required before the phone would attempt a connection.
I'm not sure if the OS determines where that set point is located or if it's something the carrier can control. If it's the carrier then maybe the Nexus 5 has a radio that isn't as efficient as other phones, and the current algorithm is pegged to the best case phone.
If anyone knows how to adjust the conditions for attempting to connect to LTE or has any ides about who does control it, I'd definitely like to know. For now, I set my phone to 2G or 3G when I'm in a poor LTE reception area (which with T-Mobile is most of the time). That actually works okay for me, but I doubt it's a solution for everyone.