The reason you're G60 is running like it is isn't because of the EPROM. There is a pressure line (small...about 1/4 inch in diameter) that feeds the Digifant control unit with the manifold pressure. The pressure line starts at the throttle body and goes to the Digifant control unit. The line needs to be exactly 1 meter long and it needs to be connected to the correct port on the throttle body. If either of these requirements are not met, the engine goes into a sort of "safe mode" where it makes the car run extremely rich. This problem happened to me. I moved the pressure line to the port right next to it and it solved the problem. I wouldn't mess with the FP or anything like that because you will encounter a lean condition once you fix the pressure line problem. I'd say it's about a 95% chance that the pressure line is your problem's source. Good luck.
