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Hello my name is ***** ***** I will help you with this issue. Here are a few suggestions to try. Cats could cause this issue for sure if they are clogged, but with the tester you should be able to read the O2 Sensor sweep. If they both sweep then you most likely do not have cat issues. Will the vehicle rev fine in park? I ask this because these engines are known for the high pressure fuel pumps going bad. This will give you the lack of acceleration you are describing. If memory serves me the V12 has one on each side and they are quite expensive to replaced. If possible I would check the fuel pressure when you are driving the vehicle to see if the fuel pressure drops.
That is a symptom when the vehicle doesn't have enough fuel pressure under load. Can you check the sweep of the O2 Sensors on your scan tool? I would not look pass the fuel pressure, it is hard to say if the fuel could be air raiding causing the popping as well.