I just got the UD-3900 for my surface pro 4, but cannot get my two extended monitors to reach a higher resolution than 1440 x 900.
For the benefit of anyone else following this thread, the original poster reached out to us directly with a PlugDebug (http://plugable.com/support/plugdebug) log file. From that file it was determined that both of the monitors connected only support a maximum resolution of 1440 x 900, so the dock is working as expected (our dock won’t allow you to exceed the maximum native resolution of a monitor).
Thank you,
Bob
Plugable Technologies
www.plugable.com/support