New Modem, New Plan, Not Getting Speeds I Paid For

So in the past couple of weeks I have made multiple changes to my internet through Xfinity. First, when my SB8200 modem was acting wonky and all of my troubleshooting didn't pan out, I went ahead and bought a new Arris S34 cable modem and set it up on my account.

Then, a week or two later, I decided to upgrade my internet speed from 500 Mbps to 1.1 Gbps (along with dropping my TV plan). I did the upgrade of internet and cancellation of TV over the phone, confirmed everything, and thought I was good to go. After that, my account showed the order as pending and I was not getting the upgraded speeds. The next day, I took my DVR box back to the local Xfinity store and mentioned that my order was still pending. The customer service agent said it was likely waiting for me to return the DVR box, typed some things into his computer, and told me I should be good by the time I got back home.

Sadly, the internet speeds had not changed when I got back to my house. On top of that, my old SB8200 modem was marked as the active one on my account and the new Arris S34 was inactive. I worked with chat support to get that fixed and hoped that would resolve the speed issue, but it didn't.

Eventually, I figured that the bottleneck was probably my WiFi 5 mesh router system. Just to make absolutely sure, I went ahead and connected my computer directly to the Arris S34 modem via Cat 6 cable. I used the 2.5 Gbps port on the Arris S34 and connected it to the same rated port on my computer. Then, I went and tried every speed test I could find - Fast.com, MLab, Xfinity, Ookla, etc. Just like before, the upload speeds matched or exceeded what's on my plan (35 Mbps). The download speeds were still all over the place, though. Depending on the test or even when I would run the same test multiple times, download speeds seemed to be all over the place. I got everything from 350 Mbps to just under 1 Gbps. Never did I get 1.1 Gbps or above.

So, with all of that said, I'm out of ideas and looking for some help. My gut is telling me that something might be wrong with the modem provisioning, but I can't prove that as far as I can tell. Any ideas on how to fix this and get me the speeds I am paying for?