LB2120 Speed Throttling

Modem LB2120.

I'm using the above modem with a t mobile sim card. And an ethernet cable to an Asus router.

The odd thing is, if I connect to the Asus router with a phone, or my PlayStation, I experience no throttling.

But when I connect my windows pc I get the 500kbs hotspot limit.

What is tmobile using to tell a windows pc is connected? And how can I get full speed like phones and my PlayStation gets?

Thanks guys for the help.