The reception on the (at least Verizon) Gnex is very inconsistent and overall poor compared to other phones in my experience. I worked in a strong 4G area and for the whole year that I had my Gnex, I would mostly stay on 3G or 1x while inside my building at my desk while I saw people with other 4G phones on Verizon have 4G signal while in the same spot. I would occasionally get 4G, but it would usually go away and revert back to 3G after a min or trying to actually connect to something. I have a friend with a Gnex that works near me too and he had the same experience. We were both rooted/ROM'd too and were on the same basebands. We would also experience random data connection drops while in a strong signal area. I could be outside and have full bars of 4G (where I normally should) and while streaming something or using the connection, my phone would randomly just drop the data connection, yet show full bars of phone signal (just with no 1x/3G/4G signal next to it). It didn't happen consistently, but probably at least 1-2 times a week.
Now I have a Note 2 and haven't had any of these issues. I have 2-3 bars of 4G at my desk at all times now and have never seen data drop where it shouldn't. So I think any reception issues on the Gnex are due to a slightly inferior antenna design on the phone. That's just my take after having the phone for a full year and having every baseband firmware available installed on it (I never really saw much of a difference after the first couple that fixed even worse data connection issues). I see you're on the GSM varient though and I haven't seen as many GSM Gnex users complain of antenna issues like the Verizon users were. So it may be less of an issue on that phone.