Welcome to Comcast, home of Xfinity.
I've been dealing with similar issues for over two years. It will always be your 3rd party equipment.....never mind that after replacing it you'll continue to have problems. I suggest one final change.... ISP.... I just ordered Centurylink @ 6Mb download (best I can get) to replace my Xfinity @100Mb; a slow internet is better than no internet.
BTW - you should check the SNR levels. In theory, values at or below 35dB indicate a potential problem though I've been having lots of problems lately with values in the 37-38 dB range.
FWIW, I see lots of T3 timeouts in my log.... lots of uncorrectable errors.... and lots of outages in the 8-10 minute range. It really strikes me as odd that my neighbor reports outages around the same times I have them; must be my modem.