Upload speeds drop to zero or near zero intermittently, making the connection unusable.

We have had two technicians come to our home in the last two weeks.  Same issue.  Upload speeds drop to near zero or actual zero.  Download speeds also slow to ~40 mbps or less. Ping times are normally 10 - 15, but recently increase to hundreds.   Sometimes Speedtest.net will just quit and say that they cannot complete the test.  Technicians say that there is nothing wrong with our setup here, but that "errors" are happening in the upload stream, and they don't know why or how.  My wife relies on this connection for her translation work, and so far we have lost hundreds of dollars in revenue from lost work due to a flaky connection.  Prior to a month ago, everything was solid and working as expected.  We have not made any changes in years with our networking gear.  Today Comcast said that there was an "outage" in our area, and wouldn't send a technician.  We don't know what to do to resolve the issue, and it looks to us like Comcast doesn't know either.