It would take a lot of investigating before I altered VE tables to "fix" a problem if the engine was stock. You're saying that the exhaust readings are showing rich, and you've reduce the delivered fuel volume? Is it about 10% on average? Because that's not that much... But if I thought there was a problem I'd confirm the rich readings using a wide band O2 or a three or four gas analyzer. You have to prove the sensor is correct. And I wouldn't be afraid to run open loop for a time as a diagnostic step. We had a six liter truck engine here yesterday which was adding fuel at idle. It had the slightest misfire which was sending unreacted O2 past the sensor, but it was very subtle with the pcm adding fuel and the desired idle at 550 rpm. Forcing the engine into open loop and clearing the long term trims made it much more obvious. Next step is basic mechanic stuff; diagnose a misfire.