I have the same router and it is very fast.
First of all, upgrade your route to latest stable release. If you don’t have custom configuration, wipe the configurations as well during the upgrade.
Once the modem is flashed with the latest firmware, make sure the SIM is fitted correctly and click Auto Setup and wait till it connects to your 5G tower. To verify that you are connected to 5G, it should give you something g similar to this:
Note: when you click Auto Setup the modem will use the 5G band and other preferences saved on the SIM to make the best decision an connect to the 5G tower with strong signal. In rare cases however you The modem connects to a not so fast 5G band. If that happens to you then you need to learn few AT commands to utilize the fastest band.