tmobile wifi gateway vs connecting with google nest mesh

I just signed up for the Home Internet and I was having the same problem of a decent signal on the first floor.  Having to put the router up high isn't the best………… I setup my Google Mesh system with 3 pods.  At first I was getting decent speeds of 30 mbs at the furthest point, but tonight it's less than 1 mbs when connected to the mesh, and I'm hardwired to the pod, but connected to the router via wifi it's around 9 mbs.  My computer connection is about 20 mbs but last night it was 40…………… I so want to dump Comcast, but I refuse to put up with buffering every few seconds…………..  the 2 week trial will be interesting……..

Do you have to disable the Tmobile Home wifi after connecting it with Google Wifi?

I've had my gateway a little over a week. I started out just plugging my existing mesh network into the gateway. I noticed that when I connected to the gateway's Wi-Fi the speeds were in the high 300s. When using the mesh Wi-Fi it was in the mid 100s, so basically half. I'm trying to find a way to extend the gateway's network using my Nest mesh system instead of having two networks.

For the record, the gateway sends a signal strong enough that I'm able to access it from anywhere in my 1200 sq ft apartment. I've never had that ability without a mesh system. The only reason I need to keep the mesh is because there are devices in other rooms that need to be plugged in to an ethernet port.