Nighthawk C7000 v2 slow wifi speed

I have Xfinity, had it for years. I have been renting XFi modem,  I have the 600MB speed package, and I religiously got over 600 MB as long as I was using the 5 GHZ wifi, and yes thats wifi. Today I decided to buy this modem to save money, it clearly shows it is capable of handling my speeds, so I get it activated and have my rented modem unactivated, and I too get max Wifi 240 MB down, no matter what device I am using, and you cant say its the distance my devices are away because I literally was getting 650 MB over WIFI right before I changed the modems, exact same computers, exact same phones, but now I get Max Wifi on 5G at 240MB and Wired it maxes at 400MB. I see the exact same issues others are having, but I can verify it must be the modem, or the config file they send to it as my devices were already verified getting the 600MB speed with Xfinity's rented modems. Is this somethinf Xfinity is doing because they do not want people to buy modem's? I'm sure they do not like that, they would much rather ream you for $14 amonth. I have had service for over 15 tears, Im sure you can add. So I am very upset and do not know what to do. This might be a class action lawsuit in the making.