I'm going to throw this out there for you to consider, as I had to investigate why my cell data (4G/LTE only) was dog-slow while at my house but quite good everywhere else. I'm on Verizon myself, and what I discovered was that, while at my house, my phone never connected to any actual cell tower. There are 2 houses in my subdivision that each have a Verizon cell extender. I ALWAYS connect to either one or the other. One of them is slightly faster than the other, but neither can match the speed of an actual cell tower. Since I don't know either of the owners of these houses with extenders, I can only guess that the slow-down is caused by whoever supplies their home internet connection.
To find out that I was connecting to cell extenders instead of a cell tower, I downloaded an app called Network Signal Info. It has a tab that will show you on a Google Map where the cell tower that you are connected to is located. Here's a screenshot showing the 2 cell extenders in my sub and indicating the one I'm currently connected to. Good luck with your issue.