I had this issue early on, but it seems to have gone away. It was bad on ED1 and with Juice Defender. Uninstalling JD helped a little, as it wasn't having to re-sync as often, but it didn't seem to be the cause. Anyway, that issue went away entirely with the EE4 update and everything was strong and reliable. It seemed to return when I flashed the 2.3.3 leak with EG2 basebands, though not as bad as ED1. Now that I'm on 2.3.4 with the EP1F radio, its just as reliable as EE4, though the signal isn't quite as strong at times. But that's only occasionally true, and doesn't affect data speeds much.
My guess is that it has to do with various baseband radio software not accurately reflecting the network in every area. Many of us had the problem with the poor ED1 software, and many saw an improvement with EE4, yet some did not. This leads me to believe that a future radio update will correct the issue for many who are still having problems. Verizon plans to bring a huge amount of new LTE markets online on the 21st, and since we already have a stable GB leak, I would expect we'll see the GB OTA with a newer radio (beyond EP1F) that will reflect the more widespread network in a week or two.
Please note that I have absolutely no inside info, I just have leaked GB and it works fine, and the July 21st date is from their Twitter feed. Anything regarding the OTA release is my speculation, but its just what makes sense to me.