I have a Lenovo 480T in an Ultra Docking station. I can get one monitor at 3840 x 2160 but the 2nd will only display at 1920 x 1080.
I'm using the two displayport connections - i've tried lowering the 3840 resolution on the one but it doesn't increase the resolution of the other.
Is the card limiting the resolution? Thanks
The issue is with the Docking Station and the monitors in use. The Docking Station is exposing two DisplayPort connectors, but these connectors are sharing one DisplayPort signal set. This means that the required bandwidth (based upon especially resolution and refresh rate) are the total of the two monitors connected and cannot exceed the maximum bandwidth of the DisplayPort 1.2 signal. If you connect a 4K monitor at 60Hz, there will not be enough bandwidth left to connect another 4K monitor and thus the reason why the second connected at 1920x1080. Two 4K monitors configured for 30Hz could have worked - and this is usually how they connect by default; I don't understand why they aren't (maybe because of design of docking station?).
You can get MST Hub-based adapters that allow you to connect two monitors to one DisplayPort 1.2 signal. You can get USB-C-to-2xDP and USB-C-to-2xHDMI adapters that can support this configuration properly. If you are going to connect 4K monitors, make sure you get an adapter that specifically says it can support 4K and Thunderbolt3. Here is the adapter I have: https://www.amazon.com/gp/product/B06XPVGQKY.
Hope this helps,