Left/Right bank running lean due to over rich correction factor?

I have a 95 3.5L. After the car gets to operating temp it starts to run rich and buck and jerk. Then after about an hour the check engine light comes on and it runs great! I know it is running rich but. I replaced the fuel pump, fuel regulator, had the injectors cleaned, new fuel filter and also throttle position sensor has been replaced. Once that check engine light comes on the computer must compensate and the darn thing runs great. Any thoughts?
I get a code 51 when i toggle the key on/off 3 times and count the check engine light blinks.
I am at a loss here folks. I DON'T trust a dealer or mechanic to help me out here.