|when you tapped the gage which would appear to be the gage is faulty. Since the gage does not go to zero but to about 1" Hg subtract 1" Hg from your readings.These gages are not expensive so you might want to try another to confirm.
The PCV test with no change indicates the the PCVs need to be serviced. If they haven't been replaced they should be even if they do not directly relate to your rough engine problem they are needed to be in good working order to pervent excess pressure in the crankcase that could cause oil to blow past the dip stick, cam and crank seals. Remember to use all Nissan PCVs and hoses to replace. The hoses have a small orifice inside that comes with the new ones. Some say that they are not needed, I say they are or Nissan wouldn't have put them there if they could save $.
Back to the main problem you still need to get the volt readings on the O2s at 2000 rpm to see if they are providing the correct low and high readings.
Have you checked the fuel pressure and for any injector leaks?
ZUL8TR in Orlando,FL