Not trying to steal your thread, just didn't want to create multiple threads for the same issue.
Having a very similar issue. I have ultimate with unlimited data. For the past week i have been getting about 1Mbps up. Had a tech come out but it was during a time that my upload was good. He said to call him if it started messing up again. It started happening again a few hours later. He said he would bring a different modem for me to try the next day, but then texted me saying i might be charged if he lets me use his modem. So I've been debating going and buying another SB6190 but didn't want to waste $100. I live a little east of OKC, 73115 area.
Hopefully we figure something out.
UPDATE: It's not the modem. I just purchased and activated a new modem but the problem persists. I have a new tech scheduled to come out Friday.