Hi there,

I thought the problem was with 4G decoding but you wrote the cards work on 1 PSU.
Maybe you're not connecting the add2PSU card like you should or it's broken?
PSU1 PERIF (molex) goes to add2PSU and PUS2 MB (mobo) goes to add2PSU.
GPU0....GPU3 8pin+risers to PUS1
GPU4 8pin+riser to PSU2

When you switch ON the power on PSU1 you should hear a "click" sound in your add2PSU (relay).

Cheers