Recommendations on modem/router for gigabit service

Hi,

I recently upgraded my Xfinity service to gigabit, as part of a triple play package that includes voice (but we do not connect to or use the voice service at all--we use only the TV & internet).

So far, the service has been okay (only). I occasionally get hickups where my Zoom calls drop out for a minute or so, and we have issues when were are doing 2 Zoom calls at the same time (which doesn't seem like it should be a problem at our level of service.)

I'm using a Motorola MT7711, combo moden and router. Now Comcast is telling me that this modem doesn't support the Gig bandwidth, and it needs to be replaced. So I have lots of questions:

1) Is there a troubleshooting guide I can look at to see why my service is spotty? (I've already followed the standard gigabyte troubleshooting guide and everything checks out)

2) Should I buy a new modem/router? And if so, do I really need to buy one with voice connection, since I'm not actually using it? And if I should buy a new one, what do you recommend? I really like the idea of combined modem/router since it seems to have fewer problems overall

I'm happy to post any details you might like on performance, if that will help with any troubleshooting. Thank you!