Weird Gigabit Issue with Mix Speed

I live in Salisbury, NC and currently have their new Gigabit line of 940/35Mbps line. Had it installed on Jan 28th and it was working great for 4 weeks! Then suddenly it got slower and slower to the point now that all 6 of my PC/Servers were capping out at 160-169Mbps. 

The modem that is used is their Technicolor TC4400 Doc 3.1

I got 4 different router ranging from AC 1750 to AC5400 with all type of config.

Also tested a few Gigabit network cards in different PC's.


Since Sunday(4/22) I have had 3 sets of tech come out to determine what the issue was. Their "test meter" when connected directly to the modem shows 940/35Mbps and even shows that when connected to my router and switch. So that was the first and second tech who complained and said it was on my end. So the third time the set of techs came out a Supervisor also tagged along. This time it also showed 940/35Mbps. So we decided to do a little more digging and I started to show him what I was seeing. (Keep in mind I also had proof screenshot and such of the speed when the service was first installed/4weeks worth).


I speed tested all my PC and Laptop connected to the switch/router. It all showed around 160ish besides one specific Workstation I had. Which was the oldest unit of them all containing a broadcom xtreme Gigabit card. Which this card was showing 940+/40+ when doing a speed test. We also tested EACH PC and laptops connected DIRECTLY to the modem and same results. We also tested with the tech guys personal and work laptops and they were barely getting 200-300Mbps. Keep in mind at this point we were even testing the site that the Spectrum $10000 Meter was connecting to. So with that other Workstation that was getting 940/35 we took that pci-e card out and threw it into another computer. We ran a few test and nothing it will still show 160ish. 


We though maybe its a Windows 10 issue?

So We took 10min to wipe 2 PC and reinstall windows 10 as a fresh slate and update all motherboard drivers. Load and behold...nothing still around 160-167Mbps. So for some odd reason this card in this OLD work station is able to obtain 940/35 but while all my other PC/Laptops and the Tech guys Laptops cant even get pass 300Mbps. Even the Techs/Supervisors are dumbfounded on what's going on. They checked all the lines and found a few hipup here and their but it didn't fix the problem. After calling tech so many times they keep telling me they do see a lot of T3/T4 time outs and when on site they are dumbfounded on the situation.


I have replaced all my network cards, routers, cat5/6/7 cables and still no luck.

I was wondering if anyone else had any kind of issues like this and found a fix. Because even if I downgrade my internet to the 200line I wont even be getting that speed.


Note: When this was setup the cable was brand new from the box in the back of the house running into the building. As for how old is the line outside...no idea.

Oh we also replaced the Modem, Power Brick for giggle sake .

Lead Moderator

Re: Weird Gigabit Issue with Mix Speed


Sorry to hear you are having a problem with the speeds. Some information to post to help your peers diagnose the issue can be found here:  DATA-TO-POST-TO-GET-HELP-FROM-THE-COMMUNITY


Thank you for your participation in the forums!


Julia R.
Spectrum-Social Media Customer Care
Lead Moderator-Community Forums

Proven Sharer

Re: Weird Gigabit Issue with Mix Speed

So far the key point is that you do measure the full 940 Mbps on both Spectrum's test device and on one of your PCs.   That shows the Spectrum network and modem are delivering data packets at the specified rate.  The fault lies in your computing equipment operating on your home LAN.  We here on the forums can try to help you find and fix the issues in your configuration, but it's not Spectrum's problem.

First, TURN OFF the WiFi radios in your router. 

Next, SHUT DOWN ALL FILE SHARING, DATA SYNCHRONIZING, AUTO-BACKUP, and CLOUD STORAGE applications, including anything from Apple, Nest, Google, Amazon/Audible, Facebook, Instagram, Microsoft OneDrive, any smart speakers, and especially Microsoft's Software Update sharing option.  Each of these steals capacity from the data connection. 

Now run the Spectrum Ookla speed test again on one of your connected devices first with the original network card and then using the 'antique' Broadcom card.  Tell us what download speed you get this time.


Re: Weird Gigabit Issue with Mix Speed

So sorry to waste everyone's time!


After sitting down for about an hour just to mess around to see if it was a windows 10 issue....


Load and Behold its a windows 10 issue!

Upon checking TCP Global Parameters

"Receive Window Auto-Tuning Level" Was Disabled

All I had to do was reenable it and that fixed it...


Apparently this was an issue when windows 10 decided to update with the Creator Update

In term disabling all my computers that got that update (Disabling Auto-Tuning)


The Workstation before that was getting the 940/35 had windows 10 update disabled from the root


So a simple command of 

Netsh Int Tcp Set Global Autotuninglevel=normal

Fixed everything



And were back and running!


Proven Sharer

Re: Weird Gigabit Issue with Mix Speed

Thanks for reporting back so quickly.  When I installed the latest Win10 update here on two separate computers, it did not try to change my ethernet driver settings.  I guess my ethernet cards are as "antique" as yours. 

So I suppose now the call desk techs will want me to eat my less than complimentary words.