I get 150 plus gb with the T-Mobile wifi. Everything in the house works great, except my laptop. It's always very slow, even when I'm next to the transponder. When I use the hot spot on my phone the computer works very fast. Is there anything I can do to make my computer like the transponder from T-Mobile better?
Copz1998 brings up a good point about DNS. Make sure that the DNS entry for your new gateway is 192.168.12.1 which is the address of the T-Mobile gateway. If you're using another DNS service, like Google, for the time being remove it from the stack and only use the “192” address. Reboot your computer and see if that helps.
Secondly, make sure you are using DHCP for obtaining an IP address. If for some reason you need a static address in your environment, first make sure you can connect to the gateway satisfactorily via DHCP. Then note the address that the gateway gave you, switch over to a static IP address with the address the gateway assigned, and configure the subnet mask to be 255.255.255.0 and the Router address as 192.168.12.1.
But first and foremost, check the DNS setting. It would explain your problem if your computer can't figure out the router’s address, or you have a conflicting DNS entry.
Is there anything I can do to make my computer like the transponder from T-Mobile better?
Replace your laptop WiFi card inexpensively with a newer version.
How to upgrade an old laptop wifi card
If a “hotspot” is working sounds like WPA/WPA2/WPA3 incompatibility. How old is the laptop? Is it WiFi 6? or a generation or 2 older.
Example, my Sony DVR has old 2.4 and WPA/WPA2 and will not connect to the gateway, router, or extenders. Not going to reconfigure network for a DVR. I can live without it!
See tomwil reply, if doable!