Have you checked to see if you US428 plugin is inserted into the PLUGIN folder of your DP3 FOLDER -
When you open DP3 and go to the BASICS menu and choose CONTROL SURFACE setup and you find that there is no US428 choice.. only HUI. That means you have forgotten to place this simple icon (that is on your Tascam US428 CD in the Digital performer folder) into the PLUGin folder - once this is done - your faders will react