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Long story short when I had a problem with my Arris SBG8300 having intermittently slow speeds. I could kind of web browse, but I had to keep hitting the refresh button and would often get a time out and after entering a web address it would often just sit their way longer than usual. When I did the speed test, it could take 5 attempts to load the page, but once loaded I'd either get a time out latency error or it would go flat out giving a higher speed than my plan is supposed to give me.
The solution was to show the Cox on site tech the hardware specs from https://arris.secure.force.com/consumers/articles/General_FAQs/SBG8300-Cable-Signal-Levels/?l=en_US&fs=RelatedArticle and asked him to change the cable signal levels for the upstream channels to between 45 and 51 (power level (dBmV)) (he really didn't think it would do anything). After doing that I had to remove the coax from the back of the modem, then do a factory reset, followed by plugging the coax back into the modem. This solved the problem for me.
I am just posting this as I spent hours on the phone talking with Cox and Arris both companies did an excellent job in helping me, but at the same time they both disagreed with each other. This solution is the one Arris gave me and worked with help form Cox's on site technician who had to put an attenuator (a little device that goes between the modem and the coax) on the back of my modem to change the signal levels to be within the hardware's specs. Hopefully this will save someone else their weekend.