are you testing over t he 2.4ghz band or the 5ghz band? 

50mbps is about all you’ll get from 2.4ghz but 5ghz should be faster. 

Hello,  I get 50 in both 2.4 and 5 ghz.  If I Attach to my D-Link Router through 2.4ghz I get the full 600mbs.

Not sure how you’re testing this but there isn’t a chance you hit 600mbps over a 2.4ghz connection. None. 

so maybe some details on how you’re actually testing speeds would be beneficial because that last statement makes me question your testing process/app/understanding. 

Hello, using speedtest at ookla, comcast, google, etc.  They all have been pretty consistent.

Again, if you’re getting 600mbps over 2.4ghz, more details are needed. Not just ookla/comcast. What device are you testing with? Is it hosting on the router? Whats hosting it? There’s zero possibility of getting 600mbps over a 2.4ghz connection. Even the latest wireless 7 devices are just hitting 150 (ish) mbps over 2.4ghz at close range. 

https://dongknows.com/netgear-orbi-970-series-wi-fi-7-mesh-review/

So while I respect that you’re having issues, something you’re doing or measuring with doesn’t add up. Especially with a device that old

I simply connect wirelessly to my SBG7600ac2 which is connected to comcast and get 50mg. When I connect wirelessly to my TP-LINK AX5400, that is hardwired to the SBG7600ac2 i reach speeds of 600mg as reported by using Speedtest. I get these results on 2 Lenovo laptops and an IPhone. There s nothing else to consider. They are simple tests over a simple configuration.

If you are experiencing interruptions on Wi-Fi connection, I would suggest changing the Wi-Fi channels.

http://arris.force.com/consumers/articles/General_FAQs/SBG7600AC2-Changing-the-Wi-Fi-Channel

Also, please let us the know the speed plan which you opted with ISP?

Hello Surfboard Moderator,

I have a 600mbps plan with my ISP, Comcast.  I have tried change channels but that does not seem to have an effect on it. I will admit I have only changed the channels sporadically; would you suggest I try each and every channel and go from there?

Thank you for your feedback.

Yes, you can try changing the channels one more time. If there are no changes on the behavior, I would suggest to contact ISP for the reprovisioning the modem.

Reprovisioning is deactivating the MAC address and reactivate the same.

Hello SURFboard Moderator

I will try changing each channel one by one to see if that has any change. I have been on several phone calls with Comcast for this issue, They have already tried reprovisioning my modem and to make a long story short, they are the ones who suggested on contact you. 

Jim - wish me luck

Hello SURFboard Moderator

I tried changing channels one by one to no improvement.  I then contacted Comcast again and asked that they reprovision my modem again to no improvement. I am out of ideas, do I consider this a failed Modem?  Your response and suggestions are much appreciated.

Jim

If you tried all the possible troubleshooting steps, I would suggest visiting www.arris.com/consumersupport for further assistance.