I have an iPhone 6 and LTE works fine most everywhere except on or around Castro Street in San Francisco. Most of the time, I can't even run a speed test since the free OOKLA app reports "Network Connectivity Issues." Other times, it's extremely high latency and low bandwidth. It's like this even though it shows 4 or 5 "dots" of LTE service. I also have a Retina Display iPad Mini with LTE service and see the same results, so I know it's not my iPhone.
When I switch off LTE and drop down to 3G on either device, I get decent data speeds (for 3G). I've also tried switching my iPhone LTE from "Voice & Data" to just "Data" with no change. I actually live a few blocks east of Castro where LTE service seems fine.
It's been like this for months. Is there some Verizon tower that serves that part of San Francisco that's either faulty or needs an upgrade?