Looks like I wont be able to stay with TMobile even though it works so well most of the time. It seems like the gateway will just get stuck on B12 with no secondary even though N41 and B2 are strong and nearby.
Locking to B12 causes my speeds to go from 600MBPS to 17MBPS. I am positive its not a congestion issue as it will happen in the middle of the night.
Restarting the gateway when its connected to B2 and N71 will reproduce the problem. This is not a tower issue. This is clearly the gateway getting stuck and is reproducible.
What a bummer.