Have you tried turning LTE off when you're in a spotty area? At my house, we are literally at the edge of LTE coverage, so I usually can only get 1 bar of LTE before dropping to 2 or 3 bars of 1x or 3G. The way the iPhone works is when it can acquire an LTE signal (or when it thinks it can) it will drop form 3G down to 1x, then go to LTE or it will sit at 1x until it fails to hook onto LTE, in which it will go to 3G (which it may take awhile to get from 1x to 3G after failing to connect to LTE).
When I enable LTE on my iPhone, it will immediately drop to 1x from 3G, and it will sit there while it tries to connect to LTE, then it fails to connect to LTE, hangs at 1x for a minute or so, realizes it was stupid for trying to connect to such a weak LTE signal, then it goes to 3G. Then, I may try to open a webpage, which causes it to go "Hey, maybe I should look for LTE again," so it drops to 1x, sits there, then goes back to 3G and doesn't load the webpage. On the other hand, when I disable LTE, my iPhone will almost immediately connect to 3G, and then data works pretty darn well! Yes, it's only 3G, but that's why I have 50 Mbps Wi-Fi
Anthony