^^ I had the EXACT same issue when I tried this right before my swap... and even made a whole thread about it
... so lemme ask you as everyone on that thread asked me: "have you connected the jumper blocks, along with the green connectors?"...LOL even though the instructions don't call for it, for 'reading' purposes.
I personally never tried it with the jumper blocks while I still had the old setup, as I got impatient and started with the actual swap. My error was identical on romraider, but the fuel pump would prime just fine. The thought of a 'locked' ECU was bugging me the whole time... but once everything was said and done, we plugged the new one in along with AVCS wires AND the jumper blocks + green connectors
... and it read/ flashed like a champ. Mine is this particular model: