Ok well that might be part of the problem. RB20 ECU's are alot more forgiving with non factory mods but because that turbo is pushing slightly more air then expected, your ecu might be adding to much fuel to compensate as a safety. Clean your AFM, replace your O2 sensor, check your filter, and do an ECU reset. This might help it
I'd still recommend Putiting it on a dyno to check AFR's at cruise and under load