ok the trees should make very little difference to your signal.I climbed up a ladder this afternoon, this is the mast as viewed from my house.
My antenna is mounted slightly left of this perspective, possibly partly obscured from the mast be the trees...
View attachment 639456
so seems like 3 has 2 x 5 MHz in 800mhz and 2 x 15 MHz in 1800mhz. So 1800mhz should give best speeds. Are you doing speedtest via WIFI or with lan cable?
If you login to 192.168.8.1 and look under the signal stats you will be able to see your signal strength.

