@TeeJayee 

It depends on how the uverse satellite boxes communitcate with the main unit.  Likely they are using the same or similar protocols that a Range Extender uses so it could simply be signal interference.  One this you can try to do is configure the Range Extender with a unique SSID like if your home network SSID is "Home" name the SSID of the extender "Home-EXT".  This fixes a lot of interferences issue customers come across.  I would note though that doing this also means you would need to manually connect to the extender when you want to use it. The configuration of the Range Extender is pretty straight forward, either it extends the same SSID or uses its own, but there is only 1 way for it to be configured in Range Extender mode.  If it setup and work the configuration should be correct.  

If you have tried that and it did not work.  The next thing i would do is contact the manufacture of the boxes or Uverse and see if those devices have any compatiblity issues with a range extender.   

Best Regards