I ask you the same questions I would ask myself. Always start at the lowest point or most basic stuff and then work towards things that are more complicated. Many times people will add things to the antenna system, thinking everything is correct when it is not. Having seen this several times makes me ask basic questions when there is a problem.

I do not have a premium 3 receiver, but would expect it to work with diseqc motor or positioner. Maybe some that do have the Premium 3 will test it with a positiner and USALS motor to make sure that the issues you have are not firmware related. It would be bad to send it back only to receive another that has the same issues. If the premium 3 works fine receiving a single satellite when connected straight to the dish antenna, and without using any diseqc 1.2 or USALS commands, or any switch commands, then I would suspect that the hardware is OK and the firmware is bad.