Unacceptable performance issues with XG2v2-P box

Our previous box was hosed during an overnight update and was stuck in a "Welcome reboot" loop the next AM. When I went to replace it, all they had at the Xfinity store was the chonky XG2v2-P box. Ever since, the performance has been abysmal! It takes forever to simply change channels, and forget about trying to watch something like Netflix or Prime. May as well run out, do a little shopping, and if you're lucky, by the time you get back, it will have locked onto the channel. It randomly hangs or starts buffering mid-movie, etc.  Was never an issue with the previous box. I already went through all the usual troubleshooting, resets and refreshes, unplugged it,  checked cables, went into the 'hidden' menu looking for errors in the tuner logs, etc.  Anyone else running into problems with this version of the box? I really don't feel like making yet another trip to the Xfinity store only to end up with the same problem. The 'Xfinity Assistant' is virtually useless for situations like this too because it only prompts  with pre-programmed questions. Next step is to get a tech out here.