Another frustrated customer - pixelation on televisions after upgrading to new wireless gateway

I'm sorry in advance because this is a rant, but I'm really curious how many other people are having a similar issue.

I recently received an email to upgrade my upgrade my Xfinity gateway in order to get faster upload speeds.  It's not really important to me, but since my gateway was five years old, I figured it might be time to replace it anyway (kind of like scheduled maintenance). I was using an XB3.

I went to an Xfinity store, and the salesperson said that I didn't qualify for an updated gateway because of my plan (150 Mbps).  She noticed that I wasn't on a contract plan, and offered the option of upgrading my speed to 300 Mbps plus Ultimate TV for an extra $10 per month.  I told her that I wasn't sure (because I generally don't like contracts) and she said that I could think about it, but not too long (the offer would still be there for a few days). She told me that I could only upgrade the gateway with a faster internet plan, and proceeded to grab a new XB3 from behind the counter for me.  It was then that I made the decision to do the internet/channel upgrade. I really only wanted to upgrade in order to get Bally Sports Detroit, which is only available on the Ultimate TV plan now.  I don't even care about the other additional channels, or the faster internet speed for that matter.  Just Bally Sports.  So I left with a faster plan, 85 extra channels, and an XB7 gateway.

So I go home happy, install the gateway, and immediately get pixelation on my televisions again (I have two).  Again, it happens at least once a minute, every minute, every hour. Refreshing / restarting the system didn't help.  Xfinity assist didn't help. No changes have been made to either TV, and neither are using any type of splitter.  There's no splitter on the gateway either.  Here's the rub: when I unplugged the power cord on the gateway, the TVs work perfectly.  No pixelation whatsoever.  

With the XB3 gateway, I would only very rarely have pixelation issues.  And usually, a system restart sorted them out.

I went back to the Xfinity store and was given an XB8 to see if it fixed things.  The salesperson (a different person) told me that if the problem wasn't fixed, to come back and he would give me an XB3 gateway. So I go home, and it's the same problems again.  Constant pixelation,which is only fixed when I power off the gateway.  This is beyond frustrating - I'm left with the option of  either having internet (but with pixelation issues on TV), or a nice clear picture (but no internet. Or no home phone either, because I have that too).  

My last resort was to go back to the Xfinity store (again!) and trying to get another XB3 (which I was told I could), to see if that would help with the pixelation issues.  I'm aware that the XB3 would lower my upload speeds, but honestly I really don't care about that.  My understanding is that I'll still get the 300 Mbsp download speed with it.  I was helped by yet anyone person, and was told that Xfinity is phasing the XB3 out.  If that's the case, why was I initially being given one as a replacement on my initial visit?  Or told that I could get one on my second visit?

This whole episode has left a real sour taste in my mouth.  I've never had much issues with Xfinity equipment before, rarely had to call customer service (which it seems you can't even do anymore).  Just quietly paid my monthly bill for 20 years.  It's left me wishing that I never received that "upgrade your gateway" email in the first place.  At this point I'd be glad to just go back to my old plan, with my old gateway.  All this frustration just to get Bally Sports, a network that I received for years.