Gig Service Consistently Getting 20-35 Mbps Download

Hello,

I just moved and signed-up for Xfinity Gig internet service. I'm using a Netgear Nighthawk CM1150V modem and Google Nest Mesh Wifi for my router. When I first set up my system I was getting 800+ Mbps (modem to router), but after about an hour it dropped to 20-35 Mbps (modem to router) and stayed there. I restarted my system (both the router and modem) and it went back up to 800+ for a little bit, then dropped back down to 20-35. It does that every time I restart the system. I have found the troubleshooting guide for gig internet service, but so far nothing has helped past a couple hours of restarting.

Thanks for the help!